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Projection Engineering, September, 1929 

Page 1 

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Vol. 1 

September, 1929 



How and Why the Talkies •. By Horatio W. Lamson 9 

The Projectionist's New Role By F. A. Jewell 13 

Acoustics of Motion Picture Theatres By John 8. Parkinson 14 

Treatment of Audio-Frequency Transmission Lines By Charles H. W. Nason 17 

Speech Interpretation in Auditoriums By E. C. Wente 19 

Television in the Making By Austin C. Lescarboura 21 

Visual Communication : A Bibliography By John P. Arnold 23 

Special Channel and New Standards for Television 25 

Television in Color By Herbert E. Ives 26 

Book Review 28 

Tinted Films for Sound Positives By Loyd A. Jones 29 

Tailor-Made Sound Reproducing Systems by Ludwig Arnson 37 

Rotating the "Wax" for Sound Pictures By L. A. Elmer 38 

Projecting Films on Metal Prisms 40 

New Musical Effects Produced by Electrical Means By Edward W. Kellogg 41 

The Acoustimeter By R. F. Norris 43 

Light-Sensitive Cells .' By John P. Arnold 44 

D epartmen ts 

News of the Industry 47 

New Developments 48 

Index of Advertisers 62 

Aviation Engineering 
Radio Engineering 
Projection Engineering 

Published Monthly by 

Bryan Davis Publishing Co., Inc. 

Publication Office — Lyon Block — Albany, N. Y. 

Chicago Office — 333 No. Michigan Ave. 
San Francisco Office: — 318 Kohl Bldg. 
Los Angeles Office — New Orpheum Bldg.. 
846 So. Broadway 

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52 Vanderbilt Ave. 
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Bryan S. Davis, 


James A. Walker, 


G. C. B. Rowe, 

Advertising Manager 

Yearly subscription rate $2.00 in U. S. 
Canada; $3.00 in foreign countries. 


^Projection Engineering, September, 1929 

Page 3 

Page 4 

Projection Engineering, September, 1929 


September, 1929 


WE sincerely trust that you will find 
this, the first issue, and the forth- 
coming issues of Projection Engi- 
neering not only to your liking, but 
of sufficient value in contents to preserve for 
reference purpose. 

It is the desire and aim of the editorial 
staff to serve each and every class of reader; 
the executives behind the industrial guns; the 
engineers in the field who are responsible for 
the rapid strides in the development of light 
and sound projection equipment; the owners 
and managers of theatres and auditoriums, 
v/ho are obviously interested in receiving 
the best possible returns from investments in 
sound and light projection equipment; to 
the projectionists themselves, who have been 
vested with a new responsibility .... the men 
in the booths who can make or break a show; 
and lastly, to the new and growing legion of 
technicians and servicemen in the field, who 
likewise do their share in keeping the show 
going at any cost. 

The staff of Projection Engineering is 
aware of the fact that to serve such a large 
and variant group is no easy task — that in 
many instances it will be difficult to draw 
the line between that which is of value to 
the field in general, and that which is not. 
In no other field is the technique .... the 
actual art itself, so closely allied to the engi- 
neering side. It is through the engineering 
developments that the art of the film, of the 
stage and of the actors themselves is greatly 
enhanced. It is important to know where the 
art begins and the engineering ends. 

If the effectiveness of a film can be increased 
by the application of various shades of color 
— color that will play upon the emotions of 
the audience, build up the psychological angle 
of each turn of the play — then it is a subject 
of interest to the whole industry, from the 
executive heads down to the theatre managers. 
But the actual engineering value of the devel- 
opment rests only in the details regarding the 
depositing of colors on film and the effect the 
colors may or may not have on such matters 

as the increase or decrease in the intensity of 
light, the effect of various shades on the oper- 
ation of the photoelectric cell, and so on. 
Thus, in an instance of this sort, it is the job 
of the editorial staff to judge, first, whether 
or not the angle and nature of the material 
is within the province of the publication, and, 
second, whether the material holds construc- 
tive value and is of sufficient importance to find 
a place in the general text section, or of news 
value and suitable for publication in the news 
section only. 

Since the true engineering phase in the light 
and sound projection field is not so clearly 
defined as it is in most other industries, it 
is not possible to maintain the same rigid edi- 
torial policy characteristic of the usual engi- 
neering publication. The matter of policy 
must rest solely on personal judgment rather 
than on a standardized routine, as the latter 
is entirely too inflexible for our purpose. 

However, the basic policy of PROJECTION 
ENGINEERING rests primarily on conservatism 
and constructiveness. Nothing is gained by 
the readers, or by ourselves, through the pub- 
lication of engineering articles of a deroga- 
tory nature, even though the facts be true. 
If criticism cannot be constructive it is not 
worthy of publication. We feel much the 
same concerning articles on new devices or 
systems, worthy or unworthy, given unright- 
ful importance through the gentle art of 
"comparison." Our principal objection to 
this class of material is that no actual infor- 
mation of value is offered. Being a tech- 
nical publication, PROJECTION ENGINEERING 
is desirous of offering to its readers the facts 
and the facts only. 

We feel that the editorial policy outlined 
is by far the fairest to the reader, the adver- 
tiser and the publication. We are intent on 
serving the field rather than catering to it. 
We can serve only by keeping the publica- 
tion clean and focusing our attention on such 
matters as specifically relate to the light and 
sound projection industries. 

M. L. MUHLEMAN, Editor. 

Projection Engineering, September, 1929 

Page 5 


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Projection Engineering, September, 1929 


The Answer to All Your "Talking Movie" Questions 





By JAMES R. CAMERON with an introduction 
by WILLIAM FOX (Fox Film Corp.) 

The Most Timely Publication in the Motion Picture Business Today 

Covers the making and showing of "Talking 
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Projection Engineering, September, 1929 

Page 7 

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Projection Engineering, September, 1929 



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Projection Engineering, September, 1929 

Page 9 

How and Why the Talkies 

A Resume of the Scientific Principles Underlying the Art of 

Sound Pictures 

By Horatio W. Lamson* 

THE keen interest shown in the 
synchronism of sound with 
motion pictures has led us to 
believe that our readers \vuuld 
welcome a resume of the scientific 
principles underlying this new art. 

The great majority of us recall, no 
doubt, how, in the early days of broad- 
casting, we were frequently enter- 
tained by "canned" music, that is, 
phonograph records broadcast over the 
air. During those years the electric 
phonograph and the modern public- 
address systems were reaching an ad- 
vanced state of perfection. It was 
only natural, then, that our motion 
picture producers, always keen for a 
new appeal to the public, should vis- 
ualize the combination of an electric 
phonograph with the public-address 
system to give a synchronized sound 
accompaniment to feature pictures in 
their theatres. All this appears 
simple, but in reality the present day 
achievements have been attained only 
by painstaking and costly experimen- 
tation. A considerable amount of 
credit for this is due to the researches 
of the Bell Telephone Laboratories 
and associated concerns. 

* Engineering Dept., General Radio Com- 

The Western Electric film record- 
ing machine which employs the 
light valve. 

Two Fundamental Systems 

There are two fundamental systems 
of synchronizing sound : first, that 
which employs a disc record similar 
to the familiar phonograph disc ; and, 
second, that which utilizes an optical 
record imprinted either along the edge 
of the motion picture film or on a 
separate film run in synchronism with 
the picture. 

A long series of factors enter into 
the satisfactory recording and repro- 
duction of sound picture entertain- 
ment by the disc process. Taken in 
sequence these are, in the studio : 

(1) A skillful rendition of the pro- 
gram by instrumental or vocal artists. 

(2) A correct treatment of the 
acoustical features of the studio. 

(3) The proper location and fidel- 
ity of the microphones. 

(4) A skillful operation of the mix- 
ing controls. 

(5) A high degree of fidelity in the 
recording amplifiers. 

(6) The perfection of the electro- 
mechanical recording device. 

(7) Care and attention in prepar- 
ing the wax record before and during 

(8) Exact synchronization of re- 
cording with photography. 

(9) The skillful reproduction of 
playing records from the original 

In the theatre : 

(10) The fidelity of the pickup or 
electrical reproducer, is a critical 

(11) Perfect synchronization must 
be maintained between the reproducer 
and the picture film projector. 

(12) Proper use of (he fader is 
essential. This device serves to shift 
from one record to the other and like- 
wise functions as a volume control. 

(13) A high degree of fidelity is re- 
quired in the reproducing amplifier 

(14) The output control panel 
must, be properly adjusted. 

(15) The loud-speaking equipment 
must li" suitable for the purpose. 

(16) A study must be made to give 
the proper acoustical treatment of the 
individual theatre. 

Frequency Band 

In order to obtain a realistic and 
pleasing reproduction throughout the 
whole theatre, it is essential that all 
these factors function to give a true 
rendering over a wide scale of fre- 
quencies and a large range of inten- 
sity levels. Good reproduction de- 

Recording equipment for sound- 
on-film system employed in RCA 
Photophone studios. The micro- 
phone at the right feeds into the 
microphone amplifier, in the black 
box, which in turn feeds into an- 
other amplifier operating the rec- 
order on the table. 

mands impartiality to frequencies 
from 50 to 5000 cycles per second. 
Decreasing the lower limit to 30 or 
25 cycles gives a noticeable improve- 
ment to certain types of music, while. 
if the upper limit be Increased to 8000 
cycles, an improvement in naturalness 
and articulation is attained. 

''(insider, for example, the specific 
problem in which the producer desires 
to furnish his audiences with :i sound 

record of a large orchestra to accom- 
pany a motion picture of Ibis orches- 
tra in action. The members of the 

Orchestra would be seated in the cus- 
tomary manner in semicircular tiers. 
Two or more cameras would be 

Page 10 

Projection Engineering, Septetnber, 1929 

brought into play, one to obtain long 
shots of the full orchestra in action 
and one or more to obtain closeups 
of various artists during the rendition 
of solo parts. These cameras must 
be installed in soundproof booths 
in order that the clicking of their 
mechanism may not be picked up 
by the microphones and reproduced 
audibly during pianissimo passages. 

The acoustical director has two 
major problems to consider. First, 
he must see that the arrangement of 
the artists and the acoustical nature 
of the studio is such that no trouble- 
some echoes or reverberations exist, 
while, on the other hand, the studio 
should not be dead enough to pro- 
duce a muffled record lacking in the 
desired brilliancy. A greater amount 
of reverberation is desired to give a 
pleasing brilliancy to an orchestral 
number that can be tolerated for the 
best articulation of solo singing or 
speech. Where both solo and orches- 
tral music occur in the same program 
a compromise is usually attained. 

Microphone Placement and 

The director's second concern is 
the proper distribution of a battery 
of microphones, similar in form to 
the broadcast studio microphones, at 
proper points around the orchestra. 
These microphones, sometimes as 
many as six in number, are connected 
to an instrument in the recording 
booth appropriately known as a 
mixer. By means of this device the 
amount of electrical energy taken 
from each individual microphone may 
be varied at will in aggregating the 
total response which is fed to the 
recording mechanism. The placing 
of the microphones and the proper 
manipulation of the mixer controls 
to give the most realistic record con- 

Above: A "variable area" film 
track, employed by RCA Photo- 
Below: A "variable density" film 
track, employed by Electrical Re- 
search Products, Inc. 

stitute an art in which proficiency 
is attained only by experience. Once 
mixed, the energy level of the ensem- 
ble can be raised or lowered, but the 
relative importance of the several in- 
struments cannot readily be varied. 

The composite electrical impulses 
are then amplified to a sufficient de- 
gree and fed into the recording 
mechanism. This is essentially a cut- 
ting stylus which is made to vibrate 
in strict accordance with the energiz- 
ing current. In the "lateral" type of 
recording, this vibration is along a 
radius of the disc record so that the 
stylus cuts a spiral groove on the 
disc of constant depth (about 
0.0025 inch) but of varying width. 
In the "hill and dale" type of record- 
ing, the vibration of the stylus is per- 
pendicular to the surface of the disc 

A.L0W LOOP SO ~>A~ Fi^.i 
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lamp socket 

Details of ERPI 
film pick-up at- 
tachment on 
Simplex Projec- 
tor. The light 
from the ex- 
citing lamp is 
brought to a 
focus on the 
film as a line 
0.001 by 0.0S0 
inch, thus cov- 
ering the record 
with an allow- 
ance of 0.010 
inch for varia- 
tion of position. 

giving a spiral groove of constant 
width but of varying depth. 

The lateral method is used almost 
exclusively in sound picture records. 
The original wax is a disc of metallic 
soap from 13 inches to 17 inches in 
diameter and about 1 inch thick. This 
is initially given a high polish and is 
then mounted horizontally on a turn- 
table driven at a uniform rate and 
synchronized with the film passing 
through the cameras. This syn- 
chronization is accomplished by elec- 
trical means of a highly technical 

Stylus Travel 

Contrary to practice with ordinary 
phonograph records, the stylus is 
made to travel outward from the 
center of the disc at such a rate that 
it cuts a spiral having the pitch of 
about one hundred turns per inch. 
The table rotates approximately 30 
revolutions per minute, which is less 
than one-half the speed of the 
ordinary phonograph. The larger 
records have a playing time of from 
eleven to twelve minutes and the 
stylus cuts its way over the wax at 
speeds -varying from 70 to 140 feet 
per minute. 

The Play-Back 

After the wax has been cut it is, 
of course, desirable to be able to 
play it at once in order to detect 
any flaws. For this purpose a 
special reproducer known as the 
play-back is employed. This is made 
extremely light so as to produce no 
appreciable wear on the relatively 
soft wax record. If the wax is 
declared satisfactory, it is then dusted 
with a fine conducting powder and 
electroplated, giving thus a negative 
copy of the wax, which is called 
the "master." By successive elec- 
troplating steps duplicates of the 
"master," known as "stampers," are 
obtained, from which large quantities 
of playing records may be pressed. 
By taking proper precautions the 
acoustical fidelity of the record is in 
no way injured during these pro- 

The Projection 

Let us now experience a quick 
transportation from the producer's 
studio to our favorite motion picture 

In the projecting booth a horizon- 
tal turntable is mounted beside each 
projection machine. This table is 
rotated by the same motor which 
drives the film through the projector 
so that, if the operator sets the 
needle of the reproducer at a marked 
point on the record coincident with 
threading a marked portion of the 
film over the driving sprocket, then 
perfect synchronism between sound 
and picture will be maintained. 

The reproducer is an electro- 
magnetic pickup device driven by the 
needle as it vibrates across the ir- 
regularities in the spiral groove on 
the record. This device is quite 

Projection Engineering, September, 1929 

Page 11 

similar in action to any of the variety 
of electrical phonograph reproducers 
on the market. It contains, however, 
a number of refinements which im- 
prove its fidelity over a wider range 
of frequency and volume. 

Change-Over and Fading 

The picture film and sound record 
are, of course, started together and 
both have the same playing time. If 
the subject be a multi-reel feature, 
as the end of the record is approached 
a duplicate projection machine and 
sound table are loaded with the suc- 
ceeding film and sound record and, 
at a given cue in the picture, are 






1 1 


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set in motion. Immediately thereafter 
the transition or "change-over" is 
made. This is done on the screen by 
closing the shutter of the expiring 
projector and instantly opening the 
shutter of the new machine. The 
change-over between the sound records 
is accomplished by a device known as 
a fader, by which the intensity of the 
response coming from the expiring 
record is reduced to zero and, subse- 
quently, the response from the new 

record is brought up to any desired 
level. This transition may be ac- 
complished gradually or rapidly, as is 
desired, and, like the change-over on 
the screen, is rarely perceptible to the 
layman in the audience. 

The Amplifiers 

The electrical impulses coming 
from the fader are then passed 
through a series of special amplifiers 
where they are enormously intensified. 
As an illustration let us consider the 
Bell Laboratories' system. This con- 
sists of three units. The first is a 
three-stage resistance-coupled ampli- 
fier employing low-power tubes ener- 
gized by direct current. The second 
unit consists of a push-pull stage of 
medium-power tubes heated by alter- 
nating current, while the third unit 
consists of a push-pull stage using 
high-power tubes energized by alterna- 
ting current. Plate potentials for all 
tubes are obtained from rectified alter- 
nating current. Small theatres re- 
quire only the first two-units, while 
large theatres take one or possibly 
two of the third type units to obtain 
sufficient volume of sound for the 
auditorium without overloading. The 
three units have an over-all gain of 
80 db, that is, they are capable of 
multiplying the energy of the repro- 
ducer one hundred million fold. 

The Loudspeakers 

The output of the last amplifier is 
brought to the output control panel 
where the energy is subdivided among 
several loudspeakers or horns, usually 
four in number. Two of these are 
placed in the orchestra pit and 
directed toward the balconies, while 
the other two are located behind the 
upper edge of the screen and directed 
downwards towards the rear floor 
seats. A small monitoring horn is 
placed in the projection booth for the 

A new type fader made by the 

General Radio Co. for General 

Talking Pictures Corp. 

convenience of the operators. A 
special type of screen, reflecting light 
well but transparent to sound, is 
desirable. The long exponential horns 
having an effective length of about 
fourteen feet are capable of receiving 
up to five watts of electrical energy 
and converting from 30 to 50 per cent, 
of it into sound. 

Provision is made on the output 
control panel for varying the amounts 
of power delivered to the individual 
horns. When the equipment is first 
installed in a theatre, a careful study 
is made and these controls are ad- 
justed in such a manner that the 
directive properties of the horns tend 
to focus the sound so as to produce 
the illusion that it is emanating from 
the center of the screen. An acousti- 
cal treatment of the theatre by the 
use of reflecting and absorbing sur- 
faces is often desirable to enhance 
this effect. Once made, Ihese adjust- 
ments are rarely changed. 

f»>*tp MM 


General layout of equipment comprising the Western Electric Sound Projector System, or ERPI. 

Page 12 

Projection Engineering, September, 1929 

Energy Levels 

The energy level of the whole re- 
producing system is controlled or- 
dinarily by the means of a fader. 
The "standard" positions of the fader 
for different records or portions of 
records are indicated by a schedule 
supplied to the operator. Varying 
local conditions, such as the size of 
the audience and so forth, often make 
a departure from standard schedule 
desirable. It is customary, therefore, 
to have two or more monitors seated 
in different parts of the house and in 
communication with the projection 
booth. These experienced individuals 
can thus transmit the request to raise 
or lower the level a point or two when 
circumstances require. 

Film Recording 

We now propose to consider the 
optical method whereby a photo- 
graphic record corresponding to the 
fluctuating sound impulses is obtained 
upon a film in the studio and subse- 
quently reproduced as sound in the 

There are two fundamental forms 
which such a film record may take. 
The one most commonly employed has 
a constant transverse width and an 
intensity or "density" which varies 
from point to point along the film in 
accordance with the frequency and 
amplitude fluctuations of the corre- 
sponding sound waves. Such a 
record is shaded in appearance and 
similar in character to a photograph 
of a heavily-banded light spectrum. 
It may be obtained by varying the 
intensity of the light source, either 
directly or indirectly, or by changing 
the effective width of the narrow slit 
opening through which the film is ex- 
posed. In either case the density 
across the record is constant at any 
given point along the film, giving thus 
the characteristic banded effect. 

In the second type of a record, a 
constant source of illumination is em- 
ployed, while the electrical impulses 
corresponding to the sound waves 
operate a mechanism that serves to 
vary the relative amount of the trans- 

The ERPI photoelectric cell ampli- 
fier. Note the suspension for ab- 
sorbing vibrations. 

verse slit which is illuminated at any 
given instant. This produces a black- 
and-white non-shaded record having 
a fine saw-tooth appearance. 

The Neon Lamp 

There are three distinct methods of 
optical recording which may be de- 
scribed here, all of which are funda- 
mently adapted to produce a banded 
type of record. 

The first makes use of the neon or 
similar type of glow lamp which is 
so well known in the art of television. 
The intensity of the light emitted by 
such a lamp can be varied rapidly 
and easily by a fluctuating voltage 
applied to it. If, now, our film is 
driven uniformly along behind a 
narrow transverse slit which is illu- 
minated on the opposite side by such 
a lamp, we have the means of pro- 
ducing a banded film record corre- 
sponding to the variations of the 
sound waves picked up by the studio 

The Light-Valve 

The second method utilizes a con- 
stant source of light and employs an 
ingenious device known as a "light- 
valve." This consists of two parallel 
duraluminum tapes each six mils 
wide and three mils thick. These 
are so placed in the optical system 
that, when at rest, they form an ef- 
fective slit which, viewed against the 
source of light, presents an opening 
two mils wide by one quarter of an 
inch long. By means of a high grade 
optical system an image of this slit 
in the light valve is thrown onto the 
film in the form of a transverse line 
of light one-eighth of an inch long 
and, normally, only one mil wide. 

The two duraluminum tapes form 
an electrical loop circuit and they are 
so located in a steady magnetic field 
that, when a pulsating current is 
passed 'through them, they move in 
opposite directions. In this manner 
the effective gap opening between the 
tapes, and, hence, the width of the 
image line on the film, is varied ac- 
cording to the frequency and ampli- 
tude of the electrical impulses. Such 
a modulation of the light gives, 
of course, the characteristic banded 
record on the moving film. We note 
that in this case the time during 
which each spot on the film is ex- 
posed to a constant light source 
varies, while in the other two meth- 
ods described each spot on the film 
record is illuminated for the same 
time interval by a modulated light 

It is found desirable in practice to 
adjust the tension on the tapes until 
they have a natural frequency of 
about 7000 cycles per second. Under 
this condition a 100 percent, modula- 
tion of the light, i. e., opening the 
valve slit to a maximum of four mils 
and just closing it completely requires 
about ten milliwatts of power at the 
lower audio frequencies and about 0.1 

milliwatt at the natural frequency of 
the tapes. 

The Kerr Cell 

A third method of optical record- 
ing utilizes an interesting device 
known as the Kerr cell. A beam of 
light of constant intensity is passed 
first through a Nicol's prism which 
polarizes the beam in a particular 
plane. It is then passed through a 
narrow gap between two electrodes 
and subsequently through a second 
Nicol's prism set at 45 degrees to 
the first. The gap between the elec- 
trodes in the Kerr cell is filled with 
nitro-benzol, a liquid which has the 
property of rotating the plane of 
polarized light passing through it 
when subjected to an electrostatic 

Illustration of the Western Electric 
"light valve." 

field to a degree proportional to the 
impressed voltage. Obviously, then, 
a modulation of the effective intensity 
of the light source may be produced 
by applying an alternating potential 
to the electrodes, so that, if we em- 
ploy a fixed transverse slit against 
the film, a banded record will result. 
The separation of the electrodes and 
the length of the light path between 
them determine the voltage necessary 
to produce 100 per cent modulation, 
i. e., variation between full transmis- 
sion and total extinction of the light. 
As in the case of the neon lamp, the 
degree of modulation of the Kerr cell 
is essentially independent of fre- 
quency, but in the Kerr cell the degree 
of modulation is proportional to a 
cosine function of the amplitude 
which, obviously, limits the usefulness 
of this device. 

In all three methods of optical 
recording the nominal effective time 
of exposure is about 1/18,000 second, 
corresponding to the nominal film 
speed of ninety feet per minute. This 
means that modulation of the record 
at a frequency of 18,000 cycles or 
higher would be nil with an increas- 
ingly better modulation as we go be- 
low 18,000 cycles. In the workable 
audio range, however, the modulation 
is satisfactory, or can be made so by 
the use of equalizers. 

The technique of studio recording 
follows along the general lines pre- 
viously described. The responses of 
the several studio microphones, prop- 

Projection Engineering, September, 1929 

Page 13 

erly mixed, are amplified sufficiently 
to operate whichever type of record- 
ing device is used. In general two 
separate film records are made, one 
for the sound and one for the photo- 
graphy. This permits a different 
technique of development for the two 
films, which is very desirable. Syn- 
chronization is accomplished by an in- 
terlocking electrical drive system, 
which contains mechanical filters in 
the drive of the sound film to main- 
tain a constant and uniform rate of 
travel past the exposure slit. 

It is customary in both disc or 
photographic recording to make two 
identical sound records and subse- 
quently to choose the better for print- 
ing the released positive films or pre- 
paring the playing records. The 
optical sound record, as printed on 
the films sent out to the theaters, 
takes the form of a strip about one- 
eighth of an inch wide along one side 
of the picture. The picture and the 
sound strip are printed separately on 
the positive film, the space occupied 
by one being shielded from the light 
while printing the other. 


Great care must be taken in select- 
ing both the positive and negative raw 
film stock to be used in sound picture 
work. Any irregularities in the trans- 
parency of the film or emulsion will, 
of course, generate unwelcome "back- 
ground" noises in the final reproduc- 

tion. While the eye can barely de- 
tect a two per cent change in film 
density, sudden irregularities of only 
one-tenth of one per cent, will give 
rise to an audible background noise. 

The Photoelectric Cell 

In reproducing the optical sound 
record in the theater we employ an- 
other device used in the art of tele- 
vision, namely, the photoelectric cell. 
When subjected to a steady polarizing 
voltage the photoelectric cell allows 
a current to flow through it which is 
proportional to the intensity of light 
falling upon the cell. A narrow trans- 
verse slit is interposed between the 
cell and a constant source of light. 
This slit extends across the portion 
of the film carrying the sound record 
so that the intensity of the light pass- 
ing at any instant into the photoelec- 
tric cell depends either upon the rela- 
tive density of the banded film back 
of the slit or upon the width of the 
"cut-off" portion of the saw-tooth 
film record at the point in question. 

Thus if the film is drawn uni- 
formly at the original speed across 
the slit we will obtain a pulsating 
current in the photoelectric cell circuit 
which will be a reproduction of the 
current in the studio microphones. 

Mechanical Filters 

When projecting a motion picture 
the film is advanced intermittently at 
the ra^e of sixteen frames per second. 

each • frame being stationary for the 
brief instant during which light is 
passing through it to the screen. 
Obviously, then, the synchronized pic- 
ture and sound record can not be 
adjacent on the film. In practice they 
are spaced about fifteen inches apart 
along the film, thereby allowing for 
a "loop" to take up the intermittent 
slack between them. Mechanical 
filters are used in the drive to insure 
an extreme uniformity of motion past 
the photoelectric cell slit. 

The electrical impulses obtained 
from the photoelectric cell are ex- 
tremely small in amplitude. A two- 
stage resistance-coupled amplifier is 
ordinarily necessary to bring them 
up to an energy level comparable with 
that obtained directly from the elec- 
tromagnetic pickup used in the disc 
method of reproducing. On account 
of the high impedance of the photo- 
electric cell circuit, it is desirable to 
build this amplifier into the same con- 
tainer which holds the photoelectric 
cell. The output of the amplifier, at 
low impedance, is then carried to the 
fader and, from this point on, the 
same speech amplifying system used 
with the disc method is employed. 
Likewise, the same technique of fader 
operation monitoring, and control of 
the out-put panel. 

In conclusion we wish to acknowl- 
edge our indebtedness to the Bell 
Laboratories Record for certain data 
used in this article. 

The Projectionist' s New Role 

Knowledge of Sound Equipment Is Important Consideration 

THE "Film Daily" sums up the 
case of sound pictures when it 
says : "The destiny of sound 
pictures, insofar as the public is 
concerned, rests weightily in the lap 
of the man in the theatre booth. The 
projectionist can make or break the 
show and therefore, his importance in 
the exhibition scheme of things should 
be realized." 

This should go on further and stale 
that the projectionist himself should 
realize the importance of his position 
and equip himself to get the mosl oul 
of the pictures which he is running on 
the apparatus at his disposal. But 
more essential than even this is his 
ability to be in a position to meet 
emergencies when they arise. 

This does not mean that the pro- 
jectionist should be a qualified elec- 
trical-acoustic engineer, but he should 
be familiar with most of the funda- 
mental principles in order to obtain 
the best results. But even more im- 
portant than that the projectionisl 
should have the ability to think and 
think fast in an emergency, as hardly 
anything ever happens that cannot be 

*Oeneral Manager, Projectionist Sound 


By F. A. Jewell* 

handled in a temporary fashion to 
keep the show going until an engineer 
or a serviceman can be called in to 
rectify the trouble permanently. 

It seems from observation that this 
new sound game has the average pro- 
jectionist baffled and when something 
happens, he becomes rattled in his 
frenzied efforts to do something and 
as a rule docs more harm than good. 

Just a Switch Unthrown 

A typical example of this follows. 
It is an actual occurrence, which cost 
the theatre a considerable amount and 
could have easily been avoided if the 
operator had used his head and not 
become excited. 

When the evening crew relieved the 
afternoon force, everything seemed to 
be in perfect working order. The 
right-hand machine was running on 
the first reel of the feature! and the 
sound was <>. K., but when reel two 
was faded over to the left -hand ma- 
chine, there was no sound. By this 
time the afternoon shil'l had lel'i and 

the evening crew tried to Locate the 

I rouble. The exciter litrlit was lil and 

burning at the proper brilliancy. The 

tubes in the amplifiers wore all going. 
No loose connections could be found 
and all the other usual examinations 
were made, but with no results. All 
of this required time and the longer 
it went the more excited the operator 
became. Added to this was the man- 
ager's ravings while the audience 
hissed, clapped and stamped. Then as 
a last resort, the operator began to 
experiment by changing tubes, photo- 
electric cells and resistances in the 
coupling between the photoelectric cell 
and the amplifier and anything else 
that, he could think of. 

The rest of the story is too sad to 
relate as it requires bul little Imagi- 
nation to realize what actually hap- 
pened. When the sound engineer ar- 
rived, il was too late to save the show 
for that nighl so the best he could do 

was to undo all the damage thai the 
operator had done by bis experiments. 
Then an Investigation was made to de- 
termine the original cause of ••no 

sound" and Ibis is what was found. 

Previous to running the feature, a 

silent comedy bad lieen run and the 
music was furnished by a non-syn- 
chronous device thai played standard 
(Continual on ixifir 20) 

Page U 

Projection Engineering, September, 1929 

Acoustics of Motion Picture Theatres 

Practical Information Pertaining to the Testing of Sound Conditions 
and Remedies for the Most Common Faults 

By John S. Parkinson* 

SO much unintelligible or mislead- 
ing information on the subject 
of acoustics, has been directed at 
the theatre owners and managers 
since the inception of the talking movie 
that it seems desirable at this time 
to try to put the subject on some sort 
of a practical basis. The average 
theatre owner is not interested in 
abstract discussions of the effects of 
frequency and phase distortion, nor 
does he care to go into the refine- 
ments of the reverberation theory. 
Absolutely all he wants to know is 
whether or not his customers can hear 
comfortably. If they cannot, he wants 
to know how to place the blame, and 
what steps to take. In view of the fact 
that his needs are so simple, it seems 
almost strange that the various firms 
interested in the subject have not suc- 
ceeded better in satisfying them. 

The answer lies in the fact that the 
talking movie arrived so suddenly that 
no one was prepared for it. Hundreds 
of theatres were confronted with prob- 
lems outside of their experience, and 
a frantic cry arose for anyone who 
could offer assistance. For a time the 
situation amounted almost to hysteria ; 
many owners were stampeded into be- 
lieving all sorts of impossible things 
about their houses. Now, however, 
the first rush of excitement has passed 
and there is time to give the matter a 
little coherent thought. As a matter 


J-4.2kT.EiSf R. CAMERON, a 
member of our editorial 
staff, has begun the prepa- 
ration of a series of spe- 
cial articles, to run exclusively 
in Projection Engineering. The 
first of the series of articles will 
appear in the forthcoming issue. 
Mr. Cameron is well known in 
the motion picture field, both 
personally and by the acknowl- 
edgment received through the 
numerous technical text books he 
has written, the most notable of 
which are, "Motion Picture Pro- 
jection" and "Motion Pictures 
With Sound." 

Mr. Cameron's articles xoill 
deal with the technical and semi- 
technical considerations of both 
light and sound projection as 
they are specifically applied to 
the art of motion pictures. — 

* Staff Acoustical Engineer, Johns-Man- 
ville Corp. 

of fact a comparatively small percent- 
age of theatres need acoustical treat- 
ment. In a much larger percentage 
flaws are apparent, but very often 
these flaws may be remedied by a few 
simple changes in apparatus or the 
furnishings. The fact remains, of 
course, that many theatres really do 
require expert advice and treatment, 
but the theatre owner or manager 

A view of the Fox Theatre in Detroit showing the areas on the ceiling 
where acoustical material was installed. 

should be able to determine himself 
whether this is the case. It is hoped 
that the data contained in the follow- 
ing paragraphs will facilitate this de- 
cision by describing a few simple 
experiments which any person can 


In order to understand the signifi- 
cance of these tests it will be neces- 
sary to review briefly the acoustical 
theory as it applies in each case. The 
most common acoustical defect is ex- 
cessive reverberation. This produces 
an overlapping of successive syllables 
and musical sounds with an attendant 
loss ini intelligibility. The time of re- 
verberation depends on the sound ab- 
sorptive qualities of the interior sur- 
faces of the room. It is influenced by 
carpets, upholstered seats, draperies, 
etc. These materials all increase the rate 
at which the sound decays, and conse- 
quently help to reduce the length of 
time during which reverberation lasts. 

Nearly every one has experienced the 
effect of excessive reverberation. A 
familiar case is the sound of one's steps 
reverberating in a long bare corridor. 
Another is that hollow lingering qual- 
ity which one's words assume when 
talking into a well or cistern. The 
opposite effect is obtained in a library 
or in the rug department of a large 
store. The difference is obvious, and 
will convey a fairly accurate idea of 
how much good hearing conditions de- 
pend on the control of reverberation. 
In a theatre this effect is most notice- 
able at the end of a sentence, or after 
an abrupt pause in the dialogue. The 
sound continues to be heard for two 
or three seconds, sometimes apparently 
in far corners of the house. This phe- 
nomenon must not be confused with 
the same defect in the apparatus. 
Sometimes too much reverberation is 
allowed in the recording, but this can 
always be detected because the resid- 
ual sound comes from the horn rather 
than from the body of the house. Re- 
verberation in the recorded sound 
causes the sensation that the horn is 

Reverberation almost always makes 
itself felt equally in all parts of the 
house. Immediately in front of the 
stage it may be drowned out by the 
blare of the speakers, but elsewhere 
it causes an almost uniform reduction 
in intelligibility. By virtue of this 
fact it can often be detected, for it is 
the only acoustical defect except cer- 
tain types of extraneous sound which 
annoys all the patrons equally. Here 
again we must except the defects in 
reproduction ; these of course will be 
equally annoying to everyone. 

Projection Engineering, September, 1929 

Page 15 

The quality of the reproduction may 
be determined if a comparative test is 
made using a person speaking instead 
of the electrical apparatus. The 
speaker should stand as close as pos- 
sible to the horns and speak with ap- 
proximately the same loudness. Ob- 
viously, if he can make himself under- 
stood without exercising any undue 
effort, the fault must lie in the repro- 
ducing apparatus. 

If hearing conditions improve as the 
size of the audience increases the 
probabilities are that the trouble may 
be laid to reverberation. A single per- 
son seated in a theatre furnishes as 
much sound absorption as 25 square 
feet of the average drapery. Large 
audiences sometimes cure excessive re- 
verberation simply by virtue of the 
tremendous area of absorptive surface 
which they furnish. For this reason it 
is useful to compare the afternoon and 
evening performances. 

The first point, then, is to check for 
reverberation. Compare a normal per- 
son's voice with the sound from the 
reproducing system, and listen for a 
"hangover" at each pause. Then ob- 
serve whether the condition varies 
with the size of the audience, or 
whether it is different in various parts 
of the house. 

Another very common acoustical 
defect is echo. This is somewhat more 
difficult to analyze than reverberation, 
but certain tests apply. Nearly every- 
one is familiar with echoes as they 
occur outdoors. They are most often 
heard when the source of sound is at 
a suitable distance from a large blank 
wall, or a steep hill or from the edge 
of a dense growth of trees. These 
echoes are more pronounced than those 
that occur inside a room because dis- 
tances are greater and there is no 
blurring by intermediate reflection 
from other walls. To produce a really 
annoying echo within a room there 
must be surfaces which will concen- 
trate the sound and raise it above the 
level of general reverberation. These 
facts furnish us a few clews on how to 
detect echoes. 

Sometimes the echo makes itself 
noticeable through an apparent stut- 
tering or blurring in the words, li 
is necessary to observe quite carefully 
whether the word is actually being 
heard twice. This effect is best ob- 
served at the end of :i phrase as In the 
case of reverberation. A similar test 
can be made if one person will stand 
iie\i to the born and clap his hands 

Sharply while some one else listens on 
the Moor of the house. If a con fusion 
of sounds ensue it. is probably only 
reverberation, but if one or more of 
the following sounds stand out sharply 
an echo is present. The listener should 
move around through the bouse and 

determine where the phenome Is 

noticeable. If the dif&CUlty is caused 
by echo only certain seats or rows of 
seats will be affected. In this regard 
the reports of patrons are often sur 
prisingly reliable. The writer has seen 
a number of theatres where the 
oat runs .if the house seemed to know 


The interior of 
the Metropoli- 
tan Theatre in 
Los Angeles. 
The installation 
of acoustical 
material in this 
theatre im- 
proved its 
acoustics to a 
great extent. 

almost exactly where the echoes were 
noticeable. These areas are generally 
characterized as "dead spots." al- 
though actual experiment usually de- 
fines them as echoes. 

The hand clap test may be made con- 
clusive if the person clapping will 
gradually increase the rate until a 
steady "putt-putt-putt-putt" like a 
motor boat exhaust results. Every 
alternate impulse will come from the 
echo. The technique consists in in- 
creasing the rate until the echo comes 
midway between the claps, at which 
point the number of reports will sud- 
denly appear to have been' doubled. 
This test will not apply, of course, to a 
condition where multiple echoes exist. 
In such a case, however, the effect is SO 
marked as to be unmistakable. It has 
been variously characterized as resem- 
bling a machine gun, the rustling of 
[eaves, and the sound of a distant 
motor boat. Perhaps the best imita- 
tion would be the sound produced by a 
number of lead shot Calling rapidly 
ami at equal intervals on a pine hoard. 
A true multiple echo is rare, however. 
so thai if the other tests described also 

fail to indicate the presence Of an 

echo it is probable thai the problem lies 


Extraneous Sound 
The theatre manager musl ftlSO 
guard against extraneous sound. Just 
as a little stray daylight or a glaring 

exit light win tend to destroy the 
image on the screen, so any Interfer- 
ing noise tends to confuse the sound 
reproduction. This extraneous sound 
may come from a score of sources 

ventilating fans, projection machinery, 
street noises, stage apparatus, or even 
from the audience itself scuffling, 
coughing, and squeaking their chairs. 
The insidious aspect of this problem 
is that very often it passes unnoticed 
beneath the level of the program. For 
example, when the ventilating fans are 
turned on the sound is at once audible, 
but after it has persisted for some lit- 
tle time the brain ceases to be con- 
scious of the noise as such and merely 
registers an increased resistance to 
hearing. It is, however, very simple to 
detect the presence of this noise once 
the attention is focused in the proper 
direction. Indeed, of all the obstacles 
which stand in the way of the average 
customer's hearing, the one which he 
should never have to face is this very 
problem of extraneous sound. 
One more acoustical problem occurs 

often enough to deserve mention here. 
II is the condition which make- 
hearing dillictilt beneath deep balconies 
and al the extreme sides and rear of 
Large theatres. The basic cause is 
faulty energy distribution. Theoreti- 
cally, for perfect acoustic conditions 
the energy should be evenly distrlb 

iited over the entire house ami should 

he sufficient ai nil iwiints for satisfac 

tory hearing. Every now ami then a 

theatre is built with certain parts of the 

In. use partly separated From the main 
body, anil often these off-set Bpaces are 
highly sound absorbent. When BUCh 
a condition occurs the sound waves arc 

damped out before they can penetrate 

to auditors in these areas, much as the 

roice U muffled in a closet full of 

Page 16 

Projection Engineering, September, 1929 

clothes or hangings. Such a condition 
is easily recognized. If the investiga- 
tor will sit in various parts of the 
house and listen to the variations in 
sound energy rather than to the actual 
words or music he will very soon be 
able to detect any marked changes in 
the loudness of the sound. Then if the 
area in question shows attenuation so 
great as to strain the hearing, we have 
conclusive evidence that the energy 
distribution is faulty. For example, 
if one walks down the aisle from the 
stage and beneath the balcony of the 
average theatre a distinct reduction 
in intensity will be noted. If this 
phenomenon is coupled with com- 
plaints against the hearing conditions 
under the balcony the case is almost 
complete. To be sure, in almost any 
auditorium the energy shows a marked 
reduction toward the rear of the house. 
The point to observe is whether this 
reduction is so great that the ear be- 
gins to have a sensation of strain, such 
as is felt when listening to a person a 
long distance away. 

These are the major acoustical prob- 
lems and the methods which can be 
used to analyze them. Once the analy- 
sis has been made more than half the 
battle is won, for then the responsi- 
bility for correction can be placed. 

The Remedies 

If the problem is one for the acousti- 
cal companies it will be desirable first 
to have the preliminary conclusions 
checked by a thorough analysis, and 
where necessary, by actual tests in the 
house. In general, however, a com- 
plete set of plans furnishes all the in- 
formation required for the analysis. If 
the problem is found to be reverbera- 
tion the solution is generally simple — 
requiring only the installation of a cer- 
tain amount of absorbent material. 
This material may take the form of 
draperies, carpets, etc., or it may be 
supplied by various commercial acous- 
tical materials. From a standpoint of 

A sound wave photograph of the reflections fron? the ceiling in a model 
section of a Chicago theatre. 

sound absorbing efficiency those ma- 
terials which are specially designed for 
the purpose are far cheaper. Sound 
absorption should always be considered 
in terms of the cost per absorption 
unit unless the installation must also 
fulfill some special requirement of de- 
sign or utility. Permanence and mainte- 
nance cost are also important, as also 
are such considerations as fire hazard 
and ease of decoration. 

Problems involving echo and so- 
called "dead spots" generally have a 
similar solution, but the material must 
be installed in the proper areas, else 
the correction is useless. To this end 
it is important to have a competent 
engineer check the analysis, since the 
determination of echoes is largely a 
matter of experience. Echoes should, 
of course, be detected and corrected 
during the process of design, but it is 
often possible to remedy the difficulty 
even after the theatre has been built. 

If the survey indicates the presence 
of extraneous sound, the discovery of 

A typical sound wave photograph showing the reflections from the walls In a 
model plan of a Chicago theatre. 

the cause generally indicates the 
remedy also. Almost always the remedy 
is suggested by common sense; there 
are really no general rules that can be 
set down. Wherever possible the sound 
should be destroyed at its source, or 
if this is not possible barriers in the 
form of doors, curtains, vestibules, etc., 
should be erected. If direct contact 
with the theatre is essential, as in the 
case of a ventilating system, the appli- 
cation of sound absorbent material 
around the source is an effective cure. 

Energy distribution and kindred 
problems must in general be turned 
over to the acoustical engineer for solu- 
tion. No single formula applies, and 
sometimes radical changes are neces- 
sary. Sometimes changes in the posi- 
tion or power of the horns will ame- 
liorate the condition. Sometimes 
changes in furnishings and draperies 
tend to improve matters. Occasionally 
the construction of suitable reinforcing 
or equalizing surfaces has provided the 
solution. But in general each new case 
calls for a different treatment. 

The point which it is wished to em- 
phasize, however, is that in all cases a 
brief preliminary survey on the part of 
the owner or manager is desirable and 
possible. The simple tests described 
require no previous experience, and ask 
no more of the ear than it is equipped 
to give. The handicap under which 
the science of acoustics has always 
labored is the universal tendency to 
place it in the realm of the unknow- 
able, if not the supernatural. But 
after all it has been developed solely 
to assist the human ear out of its var- 
ious difficulties, and what more natural 
than to ask the ear to do its share of 
the work? Once the layman realizes 
that he carries with him always two 
of the most delicate acoustical instru- 
ments ever devised he will discard the 
compound of abstractions and super- 
stitions" which has been bewildering 
him and will begin to offer the intelli- 
gent criticism which is so badly needed. 

Projection Engineering ; September, 1929 

Page 11 

Treatment of Audio-Frequency Trans- 
mission Lines 

Data on Impedance Adjusting and Equalizer Circuits to Meet Average 
Requirements of P-A and Talking Picture Installations 

WITH increased general inter- 
est in public-address systems 
and talking picture instal- 
lations some question has 
arisen as to methods of treatment for 
audio-frequency transmission lines of 
varying length. Cases of coupling such 
lines into and out of other apparatus 
have been reduced to several standard 
instances and transformers for such 
service are now commercially avail- 

While the design of impedance- 
adjusting transformers for this purpose 
is a matter of general knowledge a 
few simple rules may be helpful in 
adapting available transformers to 
special purposes and their repetition 
may not be amiss. 

For a transformer to work out of 
an impedance Z t into an impedance 

By Charles H. W. Nason * 

step-up windings or as ratios of unity 
to some fractional part thereof, as "1 
to .55" for a step-down transformer. 

In the case of high ratio step-down 
transformers the power considerations 
are the same as for all other cases in 
transformer design and the necessity 
for guarding against excessive I 2 B 
losses in the windings themselves and 
in the transmission lines through the 

tentiometer across the voice coil. The 
exact value of this resistance would 
depend upon the speaker used. The 
output device is an auto-transformer 
tapped at ten secondary points for out- 
put to from one to ten 15-ohm speak- 

Fig. 2 shows a slightly different ar- 
rangement — perhaps of not quite so 
satisfactory a nature — employing 

. : ■:, mum iiiwimnimiiiii 

Another impe- 
dance adjusting 
circuit, similar 
in form and 
adaptation to 
that of Fig. 1, 
but working 
through a 2000- 
ohm line. 






2000 OHM 

\*—o~t — i 

FIG. 2 


where "a" is the turns ratio. This 
holds good also for vacuum tube out- 
put transformers where the impedance 
of the load varies materially with the 
frequency — in moving coil speakers, 
however, the impedance/frequency 
characteristic is substantially horizon- 
tal and we may avail ourselves of the 
full portent of the fact that maximum 

use of insufficient copper becomes evi- 
dent. This is highly important in the 
case of multiple connection of moving 
coils for dynamic reproducers and only 
exceedingly heavy and short connec- 
tions should be employed. The metal 
shielded cable used in aircraft radio 
work is ideal for the purpose and will 
meet with the underwriters approval 
for theater use. 

8+ ■*- 

'TYPE 332 

- 15 OHM 


TYPE 377 - 

500 OHM 

10 STEPS .15- (6 OHMS 


Impedance ad- 
Justing circuit 
for working out 
of 250's in push- 
pull, into one or 
more dynamic 
through a 500- 
ohm line. 

inn iiiiiimiiimiimiiimiiiiiiiiiiiiii 

undistorted power output is obtainable 
when the tube works into a load im- 
pedance of twice its Rp. Hence 

2 Z, (or 2 Rp) 

= a- (2) 


Naturally in push-pull circuits the 
two Rp's are in series and the full 
turns ratio must be taken as twice the 
value for the single tube as calculated. 

Ratios for impedance coupling trans- 
formers may be written either as ratio 
of whole numbers, as "1 to 3" for 

•Chief Engineer, Sound Service. 

Impedance Adjusting Circuits 
An impedance adjusting circuit for 
working out of two 250 tabes into one. 
or more moving coil speakers, through 
a 500-ohm line is shown in Fig. 1. The 
transformers shown are of a special 
nature but are available on order from 
the manufacturer. Provision is made 
in the tube output circuit to incor- 
porate a dynamic speaker as B moni- 
tor. As a digression from the main 
subject it is suggested that an ideal 
volume control for this monitor would 
be through a rheostat in I lie fleld ex- 
citation circuit or by a 200 ohm po- 

transformers of a generally available 

Impedance adjusting transformers 
to work out of a microphone, line or 
phonograph pick-up into the grid of 
a tube are available and the existing 
transformers having variable ratios 
may often be adapted to special cases. 
For example, the OP-M^c, shown in 
the circuit in Fig. 2 might be readily 
adapted to any of the following cases : 
out of a tube into multiple magnetic 
speakers : out of a tube into moving 
coil speakers in series ; out of a tube 
into a transmission line ; out of two 
tubes in push-pull in either of the 
foregoing cases; out of a transmission 
line into the grid of a tube, out of a 
line into various combinations of mag- 
netic or moving coil speakers. In fact 
a study of the transformers now on 
the market will yield many such cases 
of adaptability. In some cases no such 
simplicity occurs — working out of a 
detector tube into a remote amplifier 
or from a microphone into lino, mixer 
or tube presents a problem noi so easily 
solved with makeshift equipment. 
Happily the Gods have been good and 
there is no lack of special transform- 
ers for such cases. 

In Fig. 3 is shown a reproduction of 
a sheet issued by one of the better 

known manufacturers, demons! ral Ing 
in part the adaptability of certain 
standard items. 

Necessary Frequency Ranges 

Transmission lines, though consist- 
ing merely of a resistance lor normal 

Page 18 

Projection Engineering, September, 1929 


PLATE a. nl/ o GRID 










0>-r°'?r < 

OP 1- OP 2 -OPS 




Jl f '. 
•SEC. o) 






B1-B2 -B3 



fc> T. t 

1-6/1 < 
° 2-7/1 L 



Fig. 3. Showing, in schematic form, a group of transformers well suited to 

meet the special requirements of audio-frequency transmission lines, etc. 

(Courtesy of Ferranti, Inc.) 

power work represent complex net- 
works for use at voice frequencies and 
are most effective filters in some cases. 
Proper and enjoyable reproduction of 
music calls for a frequency range of 
from fifty to five thousand cycles but 
the high quality reproduction of speech 
requires that the range be extended in 
the upper register to much higher on 
the scale. Recent advancements in 
wax recording make the transmission 
of frequencies in excess of eight thou- 
sand cycles a necessity if full advan- 
tage is to be taken of the new stand- 
ard of quality and if the aspirates and 
sibillants of the spoken word are to 
be fully evident. "As silent as the 
's' in 'Talkie' " is a recent "wise 
crack" amongst the Broadwayites — 
and it's no joke from the engineer's 
point of view because it's all too true 
in the majority of cases. Proper 
matching of the impedances of the 
different elements of an installation 
will take care of that — but the other 
frequencies must appear in their 
proper relations one to the other and 
to maintain an over-all response curve 
that is essentially flat. Peaks in the 
curve may be removed through the use 
of resonant circuits in shunt with the 
transmission line and tuned broadly 
to the offending frequency, the degree 
of absorption being made variable 
through the use of a variable resist- 
ance in series with the trap circuit, as 
shown in Fig. 4. The frequencies to 
which such trap circuits must be tuned 
are determined through the use of a 
beat-frequency oscillator and vacuum 
tube voltmeters. The run is coordi- 
nated on log paper, the frequency in 
cycles against the level in db's so as 
to evidence the true audibility char- 
acteristics of the system. The sche- 
matic set-up for such a run is given in 
Fig. 5 and is self-explanatory. 

Frequency Runs 

Beat-frequency oscillators are rare 
beasts and are not to be found in the 
average small laboratory. In as 
much as the sound installations in 
theaters are mainly concerned with 
operation out of a magnetic pick-up 
an alternate and simpler method is 
shown in Fig. 6. Constant velocity 

records covering the entire range of 
frequencies are now available and with 
the aid of a single vacuum tube volt- 
meter may be used to obtain a com- 
prehensive curve of any amplifier sys- 
tem. Such a curve may be plotted in 
db's above or below the output ob- 
tained at some arbitrary frequency 

Equalizer circuit to neutralize peak 
at 1000 cycles 

(400 cycles, for example). It must be 
remembered that these runs are effec- 
tive only up to the speakers and that 
over-all runs including the speakers 
are impractical save in well equipped 
laboratories — and even then are of a 
tricky nature. I think that this covers 
the field fairly well. In most of the 
installations that the author has been 
called into consultation on the out- 
standing trouble has been the utter 

absence of any attempt to equalize or 
match the line between the amplifier 
and speakers. In nearly every in- 
stance of this kind the substitution of 
a logical transformer for those fur- 
nished with the speaker at the termi- 
nation of the line has resulted in un- 
derstandable speech as opposed to un- 
intelligible mouthings. 

These few words are not to be con- 
strued as authoritative as the subject 
is too profound for the mention of 
more than a few practical facts. For 
those wishing to delve deeper into the 
subject the author suggests the pur- 
chase of "Transmission Circuits for 
Telephonic Communication," by K. S. 
Johnson, of the Bell Telephone Labora- 
tories, published by Van Nostrand. 



THERE is nothing decidely new 
or brilliant about referring to a 
phonograph record plant as a 
canning factory. However, 
when it comes to canning miscellaneous 
sounds which have nothing to do with 
building up a library of recognized 
music, we have something decidedly 
new, and that is precisely the present 
status of a present development in the 
phonograph industry. 

"Imagine if you will," states J. E. 
Smith, President, National Radio In- 
stitute of Washington, D. C, "a plant 
devoted to canning all kinds of sounds. 
Yet that is precisely what is being 
done today by certain phonograph 
record companies. The rapid growth 
of the 'talkies' has led to a healthy 
demand for all kinds of sound effects. 
Thus the phonograph companies have 
prepared special sound libraries, com- 
prising hundreds of records of sounds. 
There are barking dogs, crying babies, 
mob yells, hotel lobby backgrounds, 
sewing circle backgrounds, railway 
train, fire engine, steamship whistles, 
church bells, artillery fire, machine 
guns in action, tanks soldiers march- 
ing, etc., etc. These records are in- 
tended primarily for small theatres 
which cannot afford the synchronized 
equipment of the regular 'talkies,' but 
desire to employ records for incidental 
music, and the required sound effects." 















L - r— ' 




FIG. 6 



Fig. 5. Set-up, with beat frequency oscillator, for making frequency runs on 

transmission lines. 

Fig. 6. An alternate method for making frequency runs, using a constant 

amplitude "frequency" record. 

Projection Engineering, September, 1929 

Page 19 

Speech Interpretation in Auditoriums 

The Relation of Frequency to Articulation, the Masking of Tones and 
the Importance of Adequate Absorption Qualities 

By E. C. IVente* 

THAT different auditoriums of 
approximately the same size 
vary greatly in their acoustic 
properties is apparent even to 
the casual observer. In some halls 
it is difficult to follow a speaker who 
might be heard easily in a room with 
better acoustics. An auditorium which 
is acoustically bad for speaking pur- 
poses usually has one or the other of 
two defects ; either the speaker's voice 
is too faint at remote points, or. on 
account of excessive reflections from 
the walls, the spoken syllables do not 
reach the ears of the listener as 
articulate sounds but as a chaos of 


60 I- 



50 o 






> O006 











1000 2000 3000 4000 5000 


Fig. 1. (A) Relative energy distri- 
bution of speech at each frequency; 
(B) Per cent energy below given 

tones, from which he can extract the 
meaning only by a tiring effort. 

In the open air, words reach flic 
listener directly from the speaker ; in 
a closed room, however, they are re- 
inforced by reflection from the enclos- 
ing walls. This gives rise to the 
phenomenon that in a room a spoken 
syllable is heard for some time after 
it Is uttered, and the greater the re- 
fleeting power of its walls, the longer 
is this time of reverberation. If the 
room has hard walls the loudness of 
one syllable .'it some distance from the 
speaker may still be great enough to 
Interfere with the Interpretation of 

the succeeding syllable. There are 
I bus two extreme conditions: If the 
walls are highly absorbing, the loud- 
ness of the speech at remote parts of 
the room may be Insufficient : If the 
walls are hard, the loudness will be 
almost the same at all parts of the 
room but the excessive revcrboral ion 
will make it difficull to distinguish the 
individual syllables of the speech. Ob- 
viously in the design of an auditorium 

these two extreme conditions must be 

* Research Department, Bell Telephom 
Laboratorit s. 

Reverberation Time 

The late Professor Sabine of Har- 
vard conducted a series of noteworthy 
experiments in which he set up as a 
measure of the acoustics of an audi- 
torium the time required for the aver- 
age sound-energy density to fall to 
one millionth of (60 db. below) its 
initial value. This time is technically 
designated as the reverberation time. 
Sabine found that for a given size of 
room it has an optimum value. Most 
of his data, however, refers to sounds 
of a frequency of 512 cycles, which 
lies near the middle of the musical 
scale. The absorption of sound by 
materials, however, varies greatly with 
frequency. Hence even rooms having 
the optimum reverberation time at 512 
cycles may yet vary widely in their 
acoustic characteristics. Sabine recog- 
nized this fact, but it was not 
sufficiently stressed, especially with 
reference to the interpretation of 

Speech sounds may be regarded as 
composites of pure tones of different 
frequencies and intensities. The dis- 
tribution of energy among the com- 
ponent tones of representative English 
speech sounds throughout the fre- 
quency range from fifty to five 
thousand cycles per second has been 
determined by Crandall and Mac- 
Kenzie. 1 Their results are shown in 











1000 2000 


Fig. 2. Syllable articulation when 

energy below given frequency is 


Fig. 1. Curve A gives the relative 
amount Of energy in speech corre- 
sponding to ih«' frequency shown as 
abscissa. In the region around two 

hundred cycles I here is approximately 

forty limes as much energy as around 

fifteen hundred cycles. Curve B gives 

the energies plotted in a little differ 

cnt way. Here the ordinate gives the 
fractional pari of the energy I hat lies 
below the corresponding frequency 
plotted BS abscissa. This curve shows 
thai Bixtj per cent of the energy in 

speech lies heiow five hundred and 
'/'// »«('<■«/ it, r lew, w\. p 221, March, 

thirty-five per cent below two hun- 
dred cycles. 

Frequency Suppression and 

In view of the preceding data it 
might seem that the low frequency 
components in speech are relatively 
important. However, it has been 
shown that, although the components 
in speech lying below five hundred 
cycles are of value in preserving the 
naturalness of a speaker's voice, they 
contribute relatively little to the in- 
terpretation of speech sounds. The 
curve shown in Fig. 2 is from a paper 
by Fletcher. 2 This curve gives the per- 
centage of syllables found in the 
English language which are correctly 
understood when all the energy below 
the frequency given as abscissa is sup- 
pressed by the transmitting system. 
For example, if all the energy below 
five hundred cycles is suppressed, the 
articulation is still within two per cent 
of the maximum, although sixty per 
cent of the energy in speech lies below 
this value. This fact points to the im- 
portance of considering the absorption 
characteristic's of materials that are 
used in rooms for damping purposes. 

In Fig. 3 is shown the absorption 
curve for a layer of hair felt such as 
is frequently used for deadening rooms. 
This material is merely given as an 
example: most other types of porous 
materials used for this purpose have 
very similar absorption characteristics. 
This material is seen to have huge 

absorption in the upper but small ab- 
sorption in the lower frequency region. 
The average intensity throughout a 
room is. to a lirst approximation, in- 
versely proportional to the absorptivity 
Of all the surfaces. Hence, in a room 
with a relative large amount of por- 
ous materials, the Intensities of the 

tones of (ho higher frequencies, which 
we have seen to he important for 
articulation, are very greatly reduced 

- Journal of the VrankUn Inst., June, 1022. 





a 40 








c, C, C, c 4 c, c, 

64 126 256 512 1024 2046 


Fig. 3. Per cent absorption of hair 
felt at different frequencies. 

Page 20 

Projection Engineering, September, 1929 



re 2 

Fig. 4. The masking of a 1500-cycle 
tone by a 300-cyc!e tone. 

in comparison with those of the lower 
frequencies, which are unimportant for 
articulation. When, then, enough por- 
ous material is introduced to reduce 
the reverberation of those tones in 
which speech is rich to the point where 
it is no longer objectionable, the in- 
tensities of the important hight fre- 
quency tones may be below the thresh- 
old of audibility at remote parts of 
the room. At these points it will be 
difficult to interpret the speaker's 

Masking of Tones 

Aside from the distracting effect of 
the reverberation of low frequency 
tones, their presence in excessive 
amounts reduces the ability of the 
auditor to hear those of high fre- 
quency. It has for a long time been 
known qualitatively that the threshold 
of audibility for a given tone is raised 
by the presence of another tone, es- 
pecially if this tone be one of lower 
frequency. A quantitative study of 

this masking of one tine by another 
has been made by Wegel and Lane, 3 
from w r hose paper the curve of Fig. 4 
is taken. An ordinate of this curve 
gives the relative power of a 1500-cycle 
tone that is just audible in the presence 
of a masking tone of three hundred 
cycles having the power indicated by 
the abscissa. Unity power for either 
tone is taken as its power at the 
threshold of audibility when no other 
tone is sounded simultaneously. For 
example, when a tone of three hundred 
cycles is sounded at an intensity of 
10° times its value at the threshold 
of audibility, a fifteen hundred cycle 
tone to be heard must be 10 4 times as 
intense as when the three hundred 
cycle tone is absent. These values of 
intensities for the respective fre- 
quencies are quite possible for speech 
in a room, which has its acoustic char- 
acteristics controlled by the absorption 
of ordinary porous materials. The 
phenomenon of masking further em- 
phasizes the importance of keeping 
down the average intensity of the 
lower tones, which for articulation are 
quite unimportant and yet are deliv- 
ered in large amounts by the speaker. 

Increasing Absorption Charac- 

The conclusions here reached, while 
resting primarily on indirect data, 
seem to be borne out by experience. 
Auditoriums having the most desirable 
acoustic properties are found to be 
those which are sufficiently dead but 
are free from hangings and other 
porous materials. Many of the best 
auditoriums have a large amount of 
wood paneling. Fig. 5 gives the ab- 
sorption curve for -such paneling as de- 

termined by W. C.' Sabine. This is seen 
to be somewhat selective in favor of 
the lower frequency tones. For a room 
that is too reverberant we could thus 
hardly do better than to increase the 
absorption by covering certain of the 
walls by some kind of wooden panels. 
Unfortunately, as the absorption co- 
efficient for such panels is low, a very 
large amount of wall space would 
usually have to be covered in order to 
bring the reverberation down to a 
proper value. This the fire laws will 
not permit in many cases. It thus 
appears that there is a need for a ma- 
terial which is fire-proof, fits into the 
decorative scheme of interiors, and has 
absorption characteristics that are high 
and selective for low frequency tones. 
Having available materials of this type 
in addition to the various porous ab- 
sorbers now on the market we could 
place the problem of acoustic treatment 
of rooms on a better engineering basis. 





O 6 


UJ c 

a. D 








c 2 


C 3 C„ C 5 
256 512 1024 




; Physical Review, XXIII, February, 1924. 

Fig. 5. The per cent absorption of 
wood paneling at different frequen- 


{Continued from page 13) 
records and was operated from the 
orchestra pit. This non-sync device 
was coupled through the fader on the 
left-hand side in parallel with the left- 
hand machine through the same ampli- 
fier and speakers which were used on 
synchronized sound-on-film. Naturally 
it was in series with a switch for cut- 
ting out the non-sync device when it 
was not in use. On the fade-over from 
the silent comedy, which was being 
run on the left-hand machine, to the 
sound feature on the right-hand ma- 
chine, the switch was not thrown to 
cut out the non-sync device by the 
afternoon crew. This switch had no 
effect on the right-hand machine as it 
was only in parallel with the left-hand 
side. Therefore, sound on this ma- 
chine was O. K. and the evening crew 
took it for granted that everything 
was in running order. However, when 
they faded over to the left-hand ma- 
chine for reel two, this switch was 
still on and acted as a short circuit, 
killing the sound on this machine. 

You can attach a dozen morals to 
the story and fix the blame where you 
will, but things like this do happen 
and will continue to happen just as 
long as untrained men are in charge 
who lose their heads in an emergency. 

Another Angle 

It would be no more than proper to 
relate here a story that will contrast 
with the above in which the operator 
used his head in an emergency and 
saved the day, although this particular 
operator had very little experience in 
the operation of sound. 

The spring in the sound gate broke 
and the operator held the film in place 
with his finger until the fade-over to 
the other machine. His attempts to 
fix the spring while the other machine 
was in operation were futile, so when 
it came back to the machine on which 
the sound gate was broken, he removed 
the sound gate from the good machine 
and put it in the other. As the sound 
gates are interchangeable and can 
easily and quickly be removed for 
cleaning purposes, it caused less than 
a minute's delay and the audience was 

hardly conscious that anything had 
happened. This gave him the neces- 
sary additional time to continue his 
repairing on this broken sound gate 
and then the show continued on se- 
renely without a single call-dojvn by 
the manager, as it is doubtful if the 
manager even knew anything had 

The author is familiar with a great 
many similar cases as the above but 
in no instance dtoes he know of a single 
case that would 'he serious enough to 
stop the show, if the projectionist in 
charge had been familiar with the 
fundamental principles of sound and 
used his head. 

To sum up, it might be well to say 
that no matter how far the research 
laboratories develop sound pictures or 
how good the reproducing apparatus is, 
or how well the sound is recorded, the 
ultimate results and the heights to 
which synchronized sound pictures 
will soar, will still depend largely on 
the projectionist himself, who must 
advance himself to the place of engi- 
neer, as operating, within itself, has 
become a secondary consideration. 

Projection Engineering, September, 1929 

Page 21 

Television in the Makim 

Two Definite Schools of Research and Engineering Development, 
What They Mean to the Future of This Young Art 


By Austin C. Lescarboura 

Member, I. R. E.; Member, A. I. E. E. 

TELEVISION is far from dead. 
A year ago there was much 
shouting about television. We 
were told that television was 
just around the corner. Many of us 
expected to see the inaugural parade in 
Washington flashed on the screen of 
our combination sight and sound 
broadcast receiver. Talk, more talk, 
and still more talk — and yet nothing 
was forthcoming by way of backing up 
the talk. Finally, the talk simmered 
down. The industry assumed that 
television was simply a flash in the 
pan, quite attractive while it flared up 
and, in contradistinction, just as dead 
when it died down. And yet, to those 
privileged to peep behind the scenes, 
television is making rapid progress, 
just the same. 

As far as we can personally deter- 
mine, there are two definite schools of 
thought in this television development : 
first, there is the nothing-short-of-per- 
fection school, which is working on 
minute detail, pictures in color, and 
other attributes of ideal television. 
However, this school stops at nothing 
in the way of intricate and costly 
equipment. To begin with, wire lines, 
particularly telephone lines, are em- 
ployed, and as many of them as may 
be necessary are available for all ex- 
periments. Only too often the radio 
and motion picture industry, but more 
particularly tlie laity, gaze at our rela- 
tively crude radio television results and 
turn away in disgust, after insisting on 
drawing comparisons with the splendid 
work of the telephone engineers work- 
ing on wire television. 
Then there is the second school, 

The latest model of the Jenkins 
televisor. The Image is viewed 
through the lens set in the shadow- 
box. The buttons and crank con- 
trol the neon tube, the loud 
speaker, the motor and the fram- 
ing of the picture. 

which does not aspire so much to per- 
fection as it aspires to something that 
is simple, inexpensive, readily manu- 
factured and salable. A progressive 
element in this school is, at the present 
time, burning plenty of midnight oil 
in an attempt to place on the market a 
practical television receiver which will 
receive some sort of pictures from sight 
broadcasting station so as to launch 
television into the everyday world. To 
our way of thinking, this group is quite 
correct : we cannot start out with per- 
fect television results, any more than 
sound broadcasting started out with 
flawless loudspeaker reproduction. 
Television must develop in everyday 
use. It must be transplanted from the 
laboratory soil, where it is pampered 
and petted along, to the rugged soil of 
everyday use, if it is to develop along 
practical and commercial lines. . The 
quicker this transplanting is carried 
out, the better for all concerned. 

The Future 

It is interesting to dream about the 
future of television — for it certainly 
has a real future, no matter what may 
seem the obstacles today — and see 
where the two schools of television 
thought are bound for. 

As we see the nothing-short-of-per- 
fection school, it is largely a question 
of developing still another application 
for telephone lines. The Bell System 
has left no stone unturned in develop- 
ing additional uses for its long-distance 
lines. Sound broadcasting, which it 
helped develop through the splendid 
work of W10AF and the original net- 
work, has paid handsome tolls to the 
American Telephone & Telegraph Com- 
pany. And now, the same far-seeing 
management is looking into the possi- 
bilities of sight broadcasting, not only 
with future wire net works in mind for 
air audiences 1ml also for theatre. 
auditorium, stadium and other large 

gatherings. In other words, we believe 
thai television is going to develop in 
several different directions: first, the 

sighl broadcasting, as a supplement to 

present-day sound broadcasting; sec 

ondi.v screen presentation for large 
audiences, with the signals coming di- 
rect by w Ire net work ; i birdly, as a sup 
plementary telephone service in social 
or business life, whereby Bighl as well 

us sound will be available tO telephone 

subscribers. Lei us analyze these 
three ways and see what they may 
menu in pracl Ice : 
Future news events will he broadcast 

over wire net works to many gather 
IngS Of people In important centers. 

Thus i championship wlze flght will 

be televised and flashed over telephone 
lines to theatres, stadiums, auditor- 
iums, fair grounds and so on where- 
ever people congregate. The living pic- 
tures, "hot off the griddle," will be 
flashed on the screen much after the 
manner of the movies, except that 
there will be a red hot news value to 
the televised pictures which can never 
be claimed for the second-hand news 

The synchronous motor, scanning 
drum, and revolving switch for 
flashing the four plates of the neon 
tube, of the Jenkins televisor. The 
framing crank revolves the motor 
and drum to frame the images. 

of the movie newsreel. Whereas the 
fastest newsreel represents a matter of 
hours or days before it can be de- 
veloped printed and transported even 
by airplane to the distant audience, 
the televised news event will be 
instantaneous. We confidently pre- 
dict thai the day will come when thea- 
tres will show televised events along 
with til in news events. And of course, 
where Hie subject interest is the main 
consideration, nothing short of excel- 
lent detail, comparable with film de- 
tail, will he tolerated. Il is for this 
reason, then, that the telephone engi- 
neers are working on the basis of the 
nothing-short-of-perfection ideal. Irre- 
spective of costs, number of wire lines. 

or engineering talent required tor 
actual operation. 

II Is a l':ir cry from our simple tele- 
Vision demonstrations of today to 
something even remotely approaching 

the usual motion picture presentation. 

and yel we dare predict tiiat this school 

has an easier _ j « • I > before it thai the 

other school working for a single pic- 
ture with crude detail. I'lea-e note 
(hat the telephone engil rs have ex- 
cellent channels available for their 
transmission, as compared with the un- 
certain medium of space through which 

the other school must flash its si k <,iaK 

Again, the telephone engineers can 

make use of any number of channels, 

Page 22 

Projection Engineering, September, 1929 

D. V. Mihaly, the inventor of a 
European televisor of simplified 
design. Note the horizontal scan- 
ning disc under which is the syn- 
chronizing mechanism. 

so that an image can be broken down 
into a large number of sections, each 
of which may be flashed simultan- 
eously, for maximum detail. Mean- 
while, the other school, with very 
limited radio channels available, must 
make the most of these channels, hand- 
ling probably the entire image at one 
time as at present. 

Because of the multiplicity of chan- 
nels, the telephone engineers are essay- 
ing pictures with considerable detail, 
and even colored pictures through the 
use of color filters and color screens, 
with multiple images for the different 
primary color values. All of which is 
quite feasible with unlimited channels 
of highest efficiency. 

Television for the Home 

The school in which the radio indus- 
try must take the keenest interest, 
even if its work appears so crude just 
now, is that school endeavoring to 
evolve something commercial out of 
television. This school is working on 
images with 24 lines, 48 lines and 60 
lines. The last-mentioned screen ap- 
pears most desirable at present, for it 
includes a remarkable amount of detail 
and is certainly a marked improvement 
over the 48-line picture, although this 
point is violently contested by workers 
in the 48-line field. Nevertheless, on 
the basis of sheer logic, it stands to 
reason that an increase of one-third in 
the fineness of texture must produce a 
noticeable improvement in detail, 
everything- else being equal. 

One point generally overlooked in 
considering television images is the 
part.played by the human imagination. 
A somewhat far-fetched comparison 
will serve to make this point clear. 
When we read words, we do not read 
and sound out each letter, so as to 
identify the words themselves. In- 
stead, through long practice, we read 
purely by the general appearance of 
each word. This is called reading by 
context or general outline. Even if a 
letter is missing, we read the word just 
the same. The best proof of this is in 
proof-reading, where missing letters 
are often overlooked even by the 
trained eye. 

Much the same applies in present-day 
television. While our images for the 
present are little more than figurative 
short-hand images, our eyes and our 
imagination supply the missing details 
to a remarkable degree. By context, 
if you please, we secure a pleasing 
image even with 48 lines. One must 
see the television images for one's self 
in order to appreciate the role played 
by our imagination. Therefore, we 
predict that 48 lines will be sufficient 
to begin with, although 60 will be more 
desirable. Furthermore, by the de- 
velopment of a satisfactory television 
technique in the way of prominent de- 
tail, a postery treatment of lights and 
shadows, properly timed action and so 
on, the utmost can be made of present- 
day limitations. When we compare the 
48-line picture of television with the 
48-line half-tone of the printed picture, 
the comparison is really far-fetched. 
We are dealing with two totally differ- 
ent things, and the 48-line television 
picture is as detailed as the 80-line 
screen half-tone, because of the part 
played by lights and shadows, better 
context, and the keener imagination of 
the looker-in. 

AVhat is meant by something com- 
mercial, as applied to television? Well, 
we want a televisor, or picture mi- 
scrambler, which can be sold for say 
$200.00 or less. The associated equip- 
ment in the form of short-wave receiver 
and amplifier, naturally increases the 
cost considerably. Later, we hope to 
drop the price from $200.00 to even 
$60. It probably can be done through 
mass production, although the syn- 
chronous motor now employed must 
always remain a big item of cost, un- 
less it can be replaced by a less costly 
synchronizing means. The televisor 
must be so simple that it can be ope- 
rated by the same person who now ope- 
rates a broadcast receiver. The tele- 
vision signals must be received over a 
reasonable distance, without excessive 
regeneration or other means likely to 
introduce distortion, and properly re- 
produced. The synchronizing means 

must be reduced to simplest terms. 
The picture must be viewed by a group 
rather than by a single person. 

Silhouette Radiomovies 

All the foregoing requirements are 
being met in commercial televisors 
shortly to be placed on the market. Of 
course the pictures are going to be rela- 
tively simple, and we even dare predict 
that they will be, for the most part, 
silhouette radiomovies, although the 
same televisors will handle silhouettes 
or half-tone without change or adjust- 
ment of any kind. Silhouettes, or plain 
black-and-white signals, are simpler to 
handle, especially over the considerable 
ranges which must be covered by the 
handful of television transmitters with 
which slight broadcasting must inaugu- 
rate its regular service. 

It is often argued that the simple 
silhouette radiomovies will not have 
sufficient appeal. Here, we believe, the 
persons presenting the arguments are 
decidedly short on memory. It is not 
so long ago that sound broadcasting 
was woefully deficient. In transmit- 
ting organ selections, for instance, we 
were cutting off at about 200 cycles or 
over, at the low end of the frequency 
scale, and probably 3000 cycles at the 
high end. The result was a miserable 
reproduction, which sounded no more 
like an organ than a newborn babe 
trying to initate a basso. Yet at the 
time the novelty of sound broadcasting 
quite overshadowed all considerations 
of tonal beauty. And so it must be 
with television : the thrill of receiving 
pictures flashed through space, no mat- 
ter how crude, will carry the day. 

The main thing today in television 
development is to get something into 
the hands of the public, simultaneously 
to inaugurate a regular — not an occas- 
ional — television broadcasting service, 
and then to redouble the research and 
engineering development activities 
based in large measure on what is 
learned in everyday practice. All the 
talk in the world, all the dreaming, 
all the arguments for or against, are 

The assembly of televisors by skilled workmen in a well-known television 
plant. Eventually, the assembly will be by belt conveyors, as in the mass- 
production plants of radio receivers. 

Projection Engineering, September, 1929 

Page 23 

as nothing compared with the introduc- 
tion of the first practical televisor 
ready to receive a regular television 
broadcasting service. 

Television in the Business and 
Social World 

The third direction which television 
will take also has to do with the tele- 
phone engineers, and that is the appli- 
cation of sight transmission to individ- 
ual business and social activities.- 
Every once in a while some writer 
■enjoys a joke about the future tele- 
phone service in which we shall have 
to exercise great care in answering 
calls for fear of being televised in a 
bath tub, in a rather advanced stage of 
undress, or again amid questionable 
surroundings not agreeing altogether 
with our vocal assurances to friend 
wife at the other end of the line. Well, 
those puns are not so far-fetched. No 
doubt we shall have television as a sup- 
plementary service of the telephone, 
although we do not expect to see this 
service in every home, because of the 
considerable cost involved. More 
likely, there will be stations in differ- 
ent cities, where business men can tele- 
phone other business men, and meet 
face to face by telephone proxy, in dis- 
cussing important deals. With the 

The televisor, shown on opposite 

page, connected to a short-wave 

radio receiver. 

features quite as well as the voice be- 
fore us, it will be easier to handle busi- 
ness by telephone. 

Well, what does this all mean to the 
radio and motion picture industries? 
Answering that question, the writer 
goes on record at this time with the 
prediction that the two industries must 
adopt television and raise it to robust 
manhood. Television will pass through 
five main epochs in its rapid develop- 
ment over a period of a decade or less. 
These epochs will be : 

{a) Experimental epoch, from 
which ice are just about to emerge, 
so as to transplant our experiments 

from the laboratory to the average 

(b) First practical televisors, 
crude but interesting, from which ice 
shall obtain much practical informa- 
tion. These televisors will also call 
for regular television broadcasting, 
irrespective of the number of lookers- 

(c) Television hoic-to-make-it- 
epoch, in which the television tech- 
nique, rather than the subject matter 
of the programs, tcill prove of great- 
est interest to the public. 

(d) The epoch of television stand- 
ardized practice, with the experi- 
mental activities giving ivaij to defi- 
nite designs for mass production pro- 

(e) The incorporation of the tele- 
vision feature along with the usual 
sound broadcast receiver, with syn- 
chronised sight and sound features. 
once television has attained a com- 
parable state of perfection. 

And so, in conclusion, television is 
far from dead. Much is being done 
even though less is being said than a 
year ago. Action, rather than loose 
talk, is the order of the day. We can 
expect great things when men, tired of 
talking, get down to brass tacks. 

Visual Communication: A Bibliography 

References to the Important Works on Phototelegraphy, Television 

and Relative Subjects 

By John P. Arnold 

BIBLIOGRAPHIES do not coin- 
pare favorably with light and 
sentimental fiction as an enter- 
taining form of reading, yet 
such compilations have a superior 
merit to persons interested in any par- 
ticular art or science. They may not 
be pleasurable, but often they happen 
to be informative, and information, ii 
a Id, \\ lien it Hues i n it gel ymi 
in trouble, is likely to pul money in 
your pocket, the latter sometimes hav- 
ing the especial advantage of getting 
you out of the former. Hence it is for 
those who want to know something 
more about visual communication thai 
this bibliography has been prepared. 

The value of this present efforl will 
not be found in a complete listing of 
the books, papers, and patents refer- 
ring to the specific branches of the arl 
known as phototelegraphy and televi- 
sion. That in fad would be Impossible 
within the limits of available space, 
for the idea of the electrical trans- 
mission of scenes and their representa- 
tions is over seventy years old and its 
literature has increased to voluminous, 
if not always respectable, proportions. 

it would he of little value to Include 
much of this early literature, for the 

development of more efficient instru- 
ments and a new technique of elec- 
trical communication has rendered 
obsolete many of the previous systems, 
and hence this would only be valuable 
from the historical viewpoint. 

It may be mentioned in passing that 
this is the first extended bibliography 
of this subject which h;ts yet appeared; 
that is. at least as far as the writer is 
aware. The thoughl .also occurs this 
attempt may inspire some other person 
to sit down and compile a more com- 
plete ami more thorough one. 

In the event thai some persons may 
wish to use the present list as a 
nucleus for preparing a really com- 
plete bibliography, it should be men- 
tioned thai many of the descriptive 
articles which have appeared in the 
radio magazines in this country and 

abroad in recenl years have i o 

omitted. To supply these omissions, 

One is referred to the usual library 
indices. Doly' "Selenium: A List of 

References, 1817-1925" (published by 
the New York Public Library), the 
writer's department of photoelectric- 
ity and visual communication in 

■•Radio" (July, 1928 to date), mid the 

hooks listed herein. From these 

sources, practically the whole litera- 
ture can he recovered. 


English Press 

Baker, T. Thorne. Wireless Pictures 
and Television. New York: l». Van 
Nostra ml Co.. 1927. 188 pp. 

Blake, G. G. History of Radio Tcle- 
graphy and Telephony. London: Chap- 
man & Hall. Ltd.. 1928. loo pp. 

Pournier d'Albe, B. E. The Moon- 

Element, An Introduction to tin Won- 
ders of Selenium. New York: D^ 
Appleton & Co.. 1924. kk; int. 

I 'iii-dale. Alfred. Television. Lon- 
don. N. Y. : Pitman & Sons. 1926. 

.Jenkins. ('. Francis. Radio Vision. 
Washington, I). 0.: Jenkins Laborato- 
ries, 1928. 

Lane, Henry .Milton. The Boston 

Post Hook on Television. Boston: Posl 

Publishing Co., 1928. 35 pp. 

I.. •niier. B. T. Practical let, vision. 

London : Brnesl Benn, 1928. 175 pp. 

i Pub. also by Van Nostrand, v y. i 

Loomls, Mary Texanna. Radio 
Theory unit Operating. Washington, 

I>. C. : Loomis Pub. Company. 1<)12!». 
4th «■.!.. 992 pp. 

Martin. Marcus .1. The Electrical 
Transmission of Photographs. Lon 
don. \. Y. : Pitman & Smis. Ltd.. 1921. 
180 pp. 

Page 24 

Projection Engineering, September, 1929 

Richards, Vyvyan. From Crystal to 
Television. London: A. & C. Black, 
Ltd., 1929. 

Secor, H. Winfield and Joseph H. 
Kraus. All About Television. New 
York : Experimenter Pub. Company, 

1927. 112 pp. (Supplement, 32 pp., 
published July, 1928) 

Sheldon, H. H., and E. N. Grise- 
wood. Television. New York : D. 
Van Nostrand Co., Inc., 1929. 194 pp. 

Tiltman, Ronald F. Television for 
the Home. London : Hutchinson & Co., 

1928. 106 pp. 

Yates, Raymond F. A B C of Televi- 
sion. New York : Television Pub. 
Company., Inc., 1929. 250 pp. 

Foreign Press 

Friedel, W. Elektrisches Fernsehen, 
Fernkinematographie und Bildfern- 
iibertragung. Berlin : H. Muesser, 1925. 

Fuchs. BildertelegrapMe. Berlin : 
G. Siemens, 1926. 

Korn, Arthur. Bildtelegraphie. Ber- 
lin: Walter de Gruyter & Co., 1923. 
146 pp. 

Korn, Arthur, and B. Glatzel. Hand- 
buch der Telautographie und Photo- 
telegraphie. Leipzig : Otto Nemnich, 

Korn, Arthur, and E. Nesper. Bil- 
drunkfunk. Berlin: Julius Springer, 
1926. 101 pp. ; bibliography. 

Mihaly, Dionys von. Das elektrische 
Fernsehen und das Telehor. Berlin : 
M. Krayn, 1923. 144 pp. 2d. imp., 1926. 

Pohl, Robert. Die elektrische Fern- 
iibertragung von Bilder. Braun- 
schweig : Vieweg & Son, 1910. 45 pp. 

Ruhmer, Ernest. Das Selen und 
seine Bedeutung fur die Elektro- 
technik. Berlin : 1902. 57 pp. 


Abbreviation of Publications 

B. S. T. J. Bell System Technical 

J. A. I. E. E. Journal of the American 
Institute of Electrical 

J. O. S. A. Journal of the Optical 
Society of America. 

P. I. R. E. Proceedings of the Insti- 
tute of Radio Engineers. 

Pop. Rad. Popular Radio. 

R. News. Radio News. 

R. Broad. Radio Broadcast. 

T. S. M. P. E. Transactions of the So- 
ciety of Motion Picture 

English Press 

Armagnat, Henri. "Phototeleg- 
raphy." Smithsonian Report for 
1908, No. 1891, 197-207. (Transac- 
tion fr. Revue Scientiflque, Apr. 18, 

Baker, T. Thorne. "The telegraphy 
of photographs, wireless and by wire." 
Smithsonian Report for 1910, No. 2023, 
257-274. (Also printed in Nature, No. 
2129; Aug. 18, 1910.) 

Baker, T. Thorne. A discussion of 
synchronization. Amateur Wireless, 
June 2, 1928. (Also Television, 1, 12; 
July, 1928.) 

"Recent advances in communication 
art." J. A. I. E. E.; Dec, 1925. 

Cooley, Austin G. R. Broad., 11, 341- 
343; Oct., 1927. Ibid., 12, 23-25, 114- 
117, 296-298; Nov., Dec, 1927, and 
Feb., 1928. (Description of the Cooley 
system. ) 

Dreher, Carl. "The future of tele- 
vision." R. Broad., 11, 235-236; Aug., 

Dreher, Carl. "The place of tele- 
vision in the progress of science." R. 
Broad., 11, 167-168; July, 1927. 

Gannett, D. K., and E. I. Green. 
"Wire transmission system for tele- 
vision." B. S. T. J., 6, 616-632; Oct. 

Gray, F. "The light of a television 
eye." N. Y. Sun (Radio section) p. 
2; July 14, 1928. 

Gray, F. "The use of a moving beam 
of light to scan a scene for television." 
J. O. S. A., 16, 177-190; Mar. 1928. 

Gray, Horton and Mathes. "The 
production and utilization of television 
signals." B. S. T. J., 6, 560-603 ; Oct., 

Gray, Frank, and H. E. Ives. "Opti- 
cal conditions for direct scanning in 
television." J. 0. S. A., 17, 428^34; 
Dec, 1928. 

Hartley, R. V. L. "The transmis- 
sion of information." B. S. T. J., 7, 
535-563; July, 1928. 

Ives, Herbert E. "The alkali metal 
photoelectric cell." B. S. T. J., 5, 320- 
335; Apr., 1926. 

Ives, Herbert E. "A photoelectric 
process of halftone making applicable 
over telephone lines." J. O. S. A., 15, 
96-109; Aug., 1927. 

Ives, Herbert E. "Television." 
B. S. T. J., 6, 551-559; Oct., 1927. 

Ives, Herbert E. "Some photographic 
problems encountered in the transmis- 
sion of pictures by electricity." 
J. O. S. A., 12, 173-194; Mar., 1926. 

Ives, Herbert E. "Tone reproduction 
in the halftone photo-engraving proc- 
ess." J. O. S. A., 13, 537-552; Nov., 

Ives, Herbert E. "Phototelegraphy." 
Encyclopedia Britannica, 13th ed., 

Ives, Horton and Clarke. "The 
transmission of pictures over tele- 
phone lines." B. S. T. J., 4, 187-217; 
Apr., 1925. 

Ives, H. E. "Telephone picture 
transmission." T. S. M. P. E., 11, 82; 
Oct., 1925. 

Jenkins, C. Francis. "Prismatic 
rings." T. S. M. P. E., 11, 65; May, 

Jenkins, C. Francis. "Recent prog- 
ress in the transmission of motion 
pictures by radio." T. S. M. P. E., 11, 
81; Oct., 1923. 

Jenkins, C. Francis. "Radio 
movies." T. S. M. P. E., 11, 7; May, 

Lane, Alfred P. "The real facts 
about television." Popular Science 
Monthly, 113, 43^4; Sept., 1928. 

Lee, E. S. "Cathode-ray oscillo- 
graphs and their uses." General Elec. 
Review, 31, 404-412; Aug., 1928. 

Mead, Sallie Pero. "Phase distor- 

tion and phase distortion correction." 
B. S. T. J., 8, 195 ; Apr., 1928. 

Mills, John. "Through electrical 
eyes." Reprint of Bell Telephone 
Laboratories; Mar., 1928. 40 pp. (Pre- 
sented before Assn. of Science 
Teachers of the Middle States at At- 
lantic City, Nov. 26, 1927.) 

Nelson, Edward L. "Radio trans- 
mission for television." B. S. T. J., 6, 
633-652; Oct., 1927. 

Ranger, R. H. "Photo-radiograms." 
P. I. R. E., 14, 161-180 ; Apr., 1926. 

Stoller, H. M., and E. R. Morton. 
"Synchronization of television." B. S. 
T. J., 6, 604-615 ; Oct., 1927. 

Zworykin, V. "Facsimile picture 
transmission." P. I. R. E.. 17 : March, 

Foreign Press 

Dubois, R. "Installation telegraphi- 
que a haute frequence avec appareils 
'Teletype' realisee sur une lique de 
transmission d'energie a 60,000 volt 
de la Societe d'Electricite du Tarn." — 
(Telecommunication over the 60,000- 
volt transmission line of the Societe 
d'Electricite of Tarn.) Revue Gen. ed 
L'Electricite, 28, 997-1003; June 9, 

Liwschitz, M. "Verhalten des selbst- 
erregten Generators bei kapazitiver 
Belastung" — (Control of the speed of 
d.c. motors by means of electron 
tubes.) Wissen. Veroff aus dem 
Siemens Konzern, 6, 23-25 ; 1927. 

Schriver, O. "Uber Verstarkung in 
der Bildtelegraphie" (On amplifiers 
for picture telegraphy). Telefunken 
Zeltung, 11, 78-84; Oct., 1927. 


United States 

675,878; July 11, 1901. Michael 
Beck. Electrograph. 

844,086; Feb. 12, 1907. E. & M. 
Belin. Telegraphic picture-transmit- 
ting system. 

851,174 ; Apr. 23, 1907. Arthur Korn. 

853,755; May 14. 1907. Edouard 
Belin. Apparatus for transmitting to 
a distance real optical images. 

884,501; Apr. 14, 1908. Arthur 
Korn. Means for measuring the 
degree of exposure of a selenium cell. 

888,098; May 19, 190S. Arthur 
Korn. Automatic photo-telegraph. 

915,154; Mar. 16, 1909. E. Belin. 

939,338; Nov. 9, 1909. Gilbert Sel- 
lers. Electrical transmission of 
graphic messages. 

939,339; Nov. 9, 1909. G. Sellers. 
Electrical transmission of messages. 

968,484 ; Aug. 23, 1910. Osias Kruh. 

970,820; Sept. 20, 1910. Gustav 
Hoglund. Apparatus for reproducing 
pictures or characters. 

1,040,110; Oct. 1, 1912. A. C. and 
L. S. Andersen. System of transmit- 
ting images to a distance. 

1,070,289; Aug. 12, 1913. A. Rap- 
penecker. Telegraph apparatus. 

1,075.614; Oct. 14, 1913. Ludwig 

Projection Engineering, September, 1929 

Page 25 

Tschorner. Image-transmitting tele- 

1,135,624; Apr. 13, 1915. Boris Ros- 
ing. Electrical telescopy. 

1,141,850 ; June 1, 1915. Curt Stille. 
Image-transformer for distance photog- 

1,161,734; Nov. 23, 1915. B. Rosing. 
Art of electric telescopy. 

1,175,313 ; Mar. 14, 1916. A Sinding- 
Larsen. Transmission of pictures of 
moving objects. 

1,176,147 ; Mar. 21, 1916. Eliot Keen. 

1,176,148 ; Mar. 21, 1916. Eliot Keen. 

1,329,688; Feb. 3, 1920. Andre 
Voulgre. Television and telephoto- 
graphic apparatus. 

1,423,737 ; July 25, 1922. H. K. San- 
dell. Art of transmitting pictures and 
the like. 

1,468,542; Sept. 18, 1923. Magne 
Petersen. Copying telegraph. 

1,470,696; Oct. 16, 1923. Alexander 
Nicholson. Television. 

1,473,882 ; Nov. 13, 1923. A. Sinding- 
Larsen. Picture transmission. 

1,503,590; Aug. 5, 1924. E. Keen. 
Method and system for transmitting 
pictures to a distance. 

1,521,188; Dec. 30, 1924. C. Francis 
Jenkins. Photographing oscillating 

1,521,189; Dec. 30, 1924. C. F. Jen- 
kins. Film reception of broadcasted 

1,521,192; Dec. 30, 1924. C. F. Jen- 
kins. Electroscope picture reception. 

1,525,548; Feb. 10, 1925. C. F. Jen- 
kins. Pneumatically controlled light 

1,525.549; Feb. 10, 1925. C. F. Jen- 
kins. Radio-picture-frequency chopper. 

1,525,551; Feb. 10, 1925. C. F. Jen- 
kins. Mechanically-suspended arma- 

1.525,552: Feb. 10, 1925. C. F. Jen- 
kins. Square spotlight source. 

1,525,554; Feb. 10, 1925. Stuart 
Jenks. Electrolytic reflector. 

1,529,473; Mar. 10, 1925. Marvin 
Ferree and Joseph Wissmar. Method 
and means for transmitting pictures. 

1,530.463; Mar. 17, 1925. C. F. Jen- 
kins. Radio vision mechanism. 

1,533,422; Apr. 14, 1925. C. F. Jen- 
kins. Web-picture message transmis- 

1,544,156: June 30, 1925. C. F. .Ton- 
kins. Transmitting pictures by wire- 

1.511,157: June 30, 1925. C. F. Jen- 
kins. Radio receiving device. 

1,544,158; June ■':'». 1925. C. F. Jen- 
kins. Wireless broadcasting of pic- 

1.515,708; July 14, 1925. Doflald M. 
Terry. Transmission of pictures by 

1,546,193; July 14, 1925. A. Bisslrl. 
Live-picture production. 

1,550,270; Auk. 18, 1925. Maurice B. 
Long. Transmission of pictures by 

1,559,437; Oct. 27, 1025. ('. F. Jen- 
kins. Double Image radio picture. 

1,571,897; Feb. 2, 1026. Founder 

d'Albe. Telegraphic transmission of 
pictures and images. 

1,572,989; Feb. 16, 1926. Paid L. 
Clark. Apparatus for the electrical 
transmission of visual images. 

1,579,263; Apr. 6, 1926. Edward F. 
Watson. Electrical transmission of 

1,580,896 ; Apr. 13, 1926. H. E. Ives. 

1,590,270 ; June 29, 1926. Edward F. 
Watson. Method and apparatus for 
synchronizing in picture-transmission 

1,593,639 ; July 21, 1926. F. W. Rey- 
nolds. Optical system. 

1,593,651; July 27, 1926. Austin G. 
Cooley. Phototelegraphy. 

1,602,121; Oct. 5, 1926. G. Ramsey. 

1,606,227: Nov. 9. 1926. J. Horton, 
H. Ives and M. Long. Transmission 
of pictures by electricity. 

1,607,893 : Nov. 23, 1926. Herbert E. 
Ives. Transmission of pictures by 

1,608,527: Nov. 30, 1926. Paul 
Rainey. Facsimile telegraph system. 

1,612,005; Dec. 28, 1926. James D. 
Ellsworth. Electrical picture-trans- 
mission system. 

1,627,111; May 3, 1927. Harry Ny- 
quist. Picture-transmitting system. 

1,631.963 ; June 14, 1927. H. E. Ives. 
Transmission of pictures by electricity. 

1.647,765; Nov. 1, 1927. H. D. 
Arnold. Transmission of pictures by 

1,648,058; Nov. 8, 1927. R. D. Par- 
ker. Electrovision. 

1.64S.127: Nov. 8, 1927. H. E. Ives. 
Transmission of pictures by electricity. 

1,64S,6S7; Nov. 8, 1927. C. A. 
Hoxie. Method and apparatus for the 
transmission of pictures and views. 

1.649,309; Nov. 15, 1927. H. E. 
Ives. Photomechanical reproduction of 


Goldsmith, Alfred N. "Image trans- 
mission by radio waves." P. I. R. E., 
vol. 17; 1929. 

Horton, J. W. "The electrical trans- 
mission of pictures and images." P. I. 
R. E., vol. 17 ; 1929. 

Ives, H. E. "Television in colors." 
Bell Laboratories Record, 7, 439-444; 
July, 1929. 

Jenkins, C. Francis. "The drum 
scanner in radiomovies." P. I. R. E., 
vol. 17 ; 1929. 

Jenkins, C. Francis. "Radio movies 
and the theater." T. 8. M. P. E., 11, 
45; July, 1927. 

Jenkins, C. Francis. "Pantomime 
pictures by radio for home entertain- 
ment." T. 8. M. P. E., 12, 110; Apr, 

Jenkins, C. Francis. "Radio photo- 
graphs, radio movies, and radio 
vision." T. 8. M. P. E., No. 16, 7S ; 
May, 1923. 

Ranger, R. H. "Mechanical develop- 
ments of facsimile equipment." P. I. 
R. E., vol. 17; 1929. 

Taylor, John B. "Narrow-casting." 
T. 8. M. P. E., 11, 759 ; Sept., 1927. 

Special Channel and New Standards for Television 

IN the gradual development of tele- 
vision, still generally considered 
some time distant for commercial 
purposes except for experiment- 
ers, engineers of the Television Com- 
mittee of the R. M. A. headed by Mr. 
D. E. Replogle of New York, are keep- 
ing pace with laboratory and experi- 
mental developments of television by 
flexible standardization. Changes in 
the first television standards, evolved 
by the R. M. A. Committee at the first 
organized meeting of television engi- 
neers more than a year ago, are be- 
ing studied ;is necessary. Another 
meeting of the Committee is planned 
tbis fall. 

A separate air cliannel for a syn- 
chronizing signal for television ex- 
periments may be requested of the 
Federal Radio Commission. The R. 
.\t. A. Television Committee has rec- 
ommended thai the commission con- 
sider the advisability and possibility 

of assigning a separate channel on 
which a standard synchronizing fre- 
quency may be broadcast. The use 
of such ;i frequency would be very 
broad, it is believed, in other scien- 
tific services. Standard recommenda- 
tions relating to scanning are being 

retained for the present. The R. M. A. 
recommends thai scanning .'it the re 

ceiving end be from left to right, and 
from top to bottom in uninterrupted 
sequence, looking directly at the ob- 

Standard practices for television 
experimenters — not rigid standards 
regarding speed elements, arc being 
recommended by the R. M. A. Tele- 
vision Committee. Assuming that the 
first successful television probably 
will be from talking picture films, it 

is recommended thai experimenters 

use discs to give IS hy .".7 ' j picture 
elements, at speeds of 15," 20 and 21 
frames per second, and also 60 by 72 
at 20 and 21 frames per second. Most 
talking pictures are projected at 21 
frames per second, and a slower rate, 
it is believed, would not bring as sat- 
isfactory results, although there is 
admitted difficulty in obtaining the 
higher speed With standard motors. 

Televish ngii rs are of the 

Opinion that it is too oarh to adopt 
lived standards for disc sp I or hole 

arrangements of television transmit- 
ters, and that it is too early to impose 
rigid standards on the television an 
to which it is hoped Mini believed 
amateurs will make valuable con 
i rlbutions. 

Page 26 

Projection Engineering, September, 1929 

Television in Color 

Natural Color Television Accomplished Through the Use of Three Sets 
of Special Photoelectric Cells and Color Filters 

By Herbert E. Ives* 

OVER two years ago Bell Tele- 
phone Laboratories demon- 
strated a practical system of 
television. For the first time 
successful representations of objects 
at rest or in motion were transmitted 
electrically — over wires or through the 
ether — for considerable distances. The 
reproduction of the scene then trans- 
mitted was in monochrome — the 
orange-red color of the neon lamp. 
Recent developments of the labora- 

sium. Its active surface is sensitized 
by a complicated process using sul- 
phur vapor and oxygen instead of by 
a glow discharge of hydrogen as with 
the former type of cell. 

The response of the new cell to 
color, instead of stopping in the blue- 
green region, continues all the way to 
the deep red. Because the former po- 
tassium cells were responsive only to 
the blue end of the spectrum, objects 
of a yellowish color appeared darker 








One semi-transparent mirror reflects red light from the neon tube; one 

reflects green light from one argon tube, and through both mirrors passes 

blue light from the other argon tube. 

tories, however, have made it possible 
to reproduce scenes with their true 
color values. The appearance of real- 
ity in the reproduced scene is thus 
greatly enhanced. 

One of the most significant features 
of this new achievement is that it does 
not require completely new apparatus. 
The same light sources, driving mo- 
tors, scanning discs, synchronizing sys- 
tems, and the same type of circuit and 
method of amplification are used as in 
the monochromatic system. The only 
new features are the type and ar- 
rangements of the photoelectric cells 
at the sending end, and the type and 
arrangements of the neon and argon 
lamps at the receiving end. The out- 
standing contributions that have made 
the present achievement possible are 
a new photoelectric cell, new gas cells 
for reproducing the image, and the 
equipment associated directly with 

New Type Photo-Cell 

To render the correct tone of col- 
ored objects, it was neecssary to 
obtain photoelectric cells which — like 
the modern orthochromatic or pan- 
chromatic plate — would be sensitive 
throughout the visible spectrum. This 
requirement has been satisfactorily 
met. Through the work of A. R. Olpih 
and G. R. Stilwell a new kind of 
photoelectric cell has been developed, 
which uses sodium in place of potas- 

than they should have and the tone 
of the reproduced scene was not quite 
correct. This disadvantage applied 
particularly to persons of dark or 
tanned complexion. When the new 
cells are used in the original television 
apparatus and with yellow filters — 
similar to those used in photograph- 
ing landscapes in order to make the 

blue sky appear properly dark — this 
defect is corrected and the images as- 
sume their correct values of light and 
shade no matter what the color of the 
object or the complexion of the sitter. 
It is the availability of the new photo- 
electric cells which makes color tele- 
vision possible ' by their use. 

The development of color television 
has been greatly simplified by the fact 
that as far as the eye is concerned any 
color may be represented by the proper 
mixture of just three fundamental 
colors — red, green, and blue. This fact 
was utilized in the development of 
color photography, and all the re- 
search that had been done in that 
field was available as background for 
color television. A host of methods of 
combining the three basic colors to 
form the reproduced image was avail- 
able but, insofar as the sending or 
scanning end is concerned, a method 
was developed which has no counter- 
part in color photography. The method 
of "beam scanning"— used in the first 
television demonstration 1 — has been 

Color Filters 

To apply this method to color tele- 
vision, three sets of photoelectric cells 
are employed in place of the one set 
used before. Each of these sets is pro- 
vided with color filters made up of 

1 Bell Record, June, 1928, page 325. 

*Member of the Technical Staff, Bell 
Telephone Laboratories. 

The disc and motor drive for the color television apparatus are the same 
as for monochromatic television. The mirror and colored filters are In the 
small box behind the disc, at the right side of the cabinet. Note the dis- 
position of the tubes. 

Projection Engineering, September, 1929 

Page 27 

sheets of colored gelatine. One set 
has filters of an orange-red color 
which make the cells see things as the 
hypothetical red sensitive nerves of 
the retina see them ; another set has 
yellow-green filters to give the green 
signal, and the third set has greenish- 
blue filters which perform a corre- 
sponding function for the blue con- 
stituent of vision. The scanning disc 
and the light source are the same as 
with the beam scanning arrangement 
use in monochromatic television. The 
only difference is in the photoelectric 
cells, and thanks to the tri-chromatic 
nature of color vision, it is only neces- 
sary to have three times the number 
of cells used previously to reproduce 
all colors. Three series of television 
signals, one for each set of cells, are 
generated instead of one and three 
channels are used for the transmission 
of the television signals. 

The photoelectric cell container, or 
"cage," has been built in a somewhat 
different form from that used in our 
first demonstration. There three cells 
were used arranged in an inverted 
"U" in a plane in front of the object. 
In the new photo-cell cage twenty four 
cells are employed, two with "blue" 
filters, eight with "green" filters, and 
fourteen with "red" filters. These 
numbers are so chosen with respect to 
the relative sensitiveness of the cells 
to different colors that the photoelec- ■ 
trie signals are of about equal value 
for the three colors. The cells are 
placed in three banks, one bank in 
front of and above the position of the 
scanned object, one bank diagonally 
to the right, and another bank diag- 
onally to the left, so that the cells 
receive light from both sides of the 
object and above. In placing the cells 
they are so distributed by color as to 
give no predominance in any direction 


The complete 
apparatus at 
the receiving 
end. On the 
left is the syn- 
c h ronizing 
panel and on 
the right are 
the amplifiers 
for three chan- 
nels. In the 
center is the 
cabinet con- 
taining the 
scanning disc, 
the argon and 
neon lamps, and 
the color filters. 


to any color. In addition large sheets 
of rough pressed glass are set up some 
distance in front of the cell contain- 
ers so that the light reflected from the 
object to the cells is well diffused. 

The television signals produced in 
the color sensitive photoelectric cells 
through the color filters are no dif- 
ferent electrically from those used in 
monochromatic television. Three sets 
of amplifiers are required, one for 
each color, and three communication 
channels in place of one, but the com- 
munication channels are exactly sim- 
ilar to those which were used with the 
same scanning disc before. 

For color television the three im- 
ages must be received in their appro- 
priate colors, and viewed simultane- 

Sido view of sending apparatus with cabinet doors removed. With the 

exception of the photoelectric cabinet at the left, the apparatus is identical 

with that used for monochromatic television. 

ously and in superposition. The first 
problem was to find light sources 
which, like the neon lamp previously 
used, would respond with the requisite 
fidelity to the high-frequency signals 
of television, and at the same time 
give red, green, and blue light. "With 
such lamps available a decision would 
have to be made as to how the three 
colors could best be combined to form 
a single image. 

Methods of Reception 

Several methods of reception are 
possible. For displaying the transmit- 
ted image to a large audience a grid 2 
could be employed similar to that used 
for the earlier demonstration but it 
would consist of three parallel tubes 
instead of a single one. 

Thus far the television images have 
been received in a manner similar 
essentially to our method for mono- 
chromatic television. The surface of 
a disc similar to that used at the 
sending end is viewed, and the light 
Prom the receiving lamp is focussed 
on the pupil of the observer's eye by 
suitable lenses. To combine the light 
cf the three lamps, they are placed at 
some distance behind the scanning disc 
and two semi-transparent mirrors are 
set up at righl angles to each other 
bul each at 45° to the line of Bight. 
| 'iic lamp is then viewed directly 
through both mirrors and one lamp is 
seen by reflection from each, as Illus- 
trated by the accompanying diagram. 
The matter of suitable lamps to 

provide die red, green, ami bine light 

lias required a great deal of study. 
There is no difficulty about the red 
lighl because (he neon gj 0w lum p 
which has been used previously in 
television can be transformed into a 

suitable red light by Interposing a red 

Idler. For the sources of green and 
blue light nothing nearly so efflcienl 

i ll< II Rrmnl. Man. 1027, pnfjr 819. 

Page 28 

Projection Engineering, September, 1929 

as the neon lamp was available. The 
decision finally made was to use an- 
other one of the noble gases — argon 
— which has a very considerable num- 
ber of emission lines in the blue and 
green region of the spectrum. Two 
argon lamps are employed, one with 
a blue filter to transmit the blue lines 
and one with a green filter transparent 
to the green lines of its spectrum. 

These argon lamps unfortunately 
are not nearly so bright as neon lamps 
and it was, therefore, necessary to use 
various expedients to increase their 
effective brilliancy. Special lamps to 
work at high current densities were 
constructed with long narrow and 
hollow cathodes so that streams of 
cold water could cool them. The cath- 
ode is viewed end-on. This greatly 
foreshortens the thin glowing layer of 
gas and thus increases its apparent 
brightness. Even so it is necessary to 
operate these lamps from a special 
"I" tube amplifier to obtain currents 
as high as 200 milliamperes. 

The receiving apparatus at present 
consists of one of the 16 inch tele- 
vision discs used in our earlier ex- 
perimental work. Behind it are the 
three special lamps and a lens system 

which focusses the light into a small 
aperture in front of the disc. The ob- 
server looking into this aperture re- 
ceives, through each hole of the disc 

T 7, 

" // 











c.« s ^ 

How the grouping of the colored 

filters before the color-sensitive 

photoelectric cells is arranged. 

as it passes by, light from the three 
lamps — each controlled by its appro- 
priate signal from the sending end. 
When the intensities of the three 
images are properly adjusted he there- 
fore sees an image in its true colors, 
and with the general appearance of 
a small colored motion picture. 

Difficulties Presented 

Satisfactory television in colors is a 
far more difficult task than is mono- 
chromatic television. Errors of qual- 
ity which would pass unnoticed in an 
image of only one color may be fatal 
to true color reproduction where three 
such images are superimposed and 
viewed simultaneously. In three-color 
television any deviations from correct 
tone rendering throw out the balance 
of the colors so that while the three 
images might be adjusted to give cer- 
tain colors properly, others would 
suffer from excess or deficiency of 
certain of the constituents. A further 
source of erroneous color exists at the 
scanning end. If the light from the 
object were not distributed equally to 
all the cells, the object would appear 
as if illuminated by lights of different, 
colors shining on it from different 

Color television constitutes a defi- 
nite further step in the solution of the 
many problems presented in the elec- 
trical communication of images. It is, 
however, obviously more expensive as 
well as more difficult than the earlier 
monochromatic form, involving extra 
communication channels as well as 
additional apparatus. 

vey Fletcher, Ph.D., Director of 
Acoustical Research, Bell Telephone 
Laboratories. 331 pages. Illustrated. 
6x9 inches. Stiff buckram binding. 
Published by D. Van Nostrand Co., 
Inc., Neiv York City. Price, $5.50. 

If the average engineer employed in the 
radio industry were asked something about 
sound he would very likely give you a 
more or less learned dissertation on the 
frequencies which he has encountered in his 
work and let it go at that. He would 
know, for example, that a loudspeaker, for 
effective operation, must reproduce a band 
of frequencies covering the musical range, 
with audibility. But, that is only the 
start of the story. 

Dr. Fletcher, who for thirteen years has 
been studying sounds, how they are made 
and heard, covers in this book many facts 
that the radio engineer should know, 
whether he designs sets, loudspeakers, or 
collects his paycheck from a broadcast 
station. Dr. Fletcher's presentation of his 
subject is most clear and interestingly 
written ; well illustrated by curves and 
tables, and where mathematical formulae 
are necessary for clarity, they are wisely 

"Speech and Hearing" is divided into 
four parts : Speech ; Music and Noise ; 
Hearing, and The Perception of Speech 
and Music. 

The opening chapter discusses the be- 
ginnings and the evolution of language, the 
functions of the lungs, vocal cords, and 
other organs of speech, the principal Eng- 
lish speech sounds and their formations, 
artificial speech sounds — their production, 
and the artificial larynx. 

Chapter two is devoted to the recording 
and characteristics of speech waves ; to 
the principles, development, and operation 
of such recording instruments as Koenig's 
"phonoautograph," Miller's "phonodeik," 
the phonograph, and the oscillograph ; to 
the differentiation of speech sound ; the 
general characteristics of speech ; and to 
tabular data showing these characteristics. 

The third chapter deals with speech 
power. The various kinds of speech power 
and the units expressing difference in 

speech powers are defined. The power re- 
quired in producing speech sounds is dis- 
cussed, and something of the manner in 
which this power is determined is ex- 
plained. The chapter closes with a section 
on the distribution of speech power into 
frequency bands. 

Chapter four develops the frequency with 
which speech sounds occur under the head- 
ings of words, syllable combinations, and 
fundamental sounds. Tables are included 
that show relative frequencies of occur- 

The opening chapter of Part Two takes 
up the characteristics of typical music 
sound waves, the operation of the electrical 
harmonic analyzer, the determination of 
acoustic spectra of musical instruments, 
and musical range and intensity. 

The second chapter affords a treatment 
of noise ; its physical properties, methods 
for its measurement, and the results ob- 
tained from noise surveys. 

The third section begins with an ex- 
planation of the mechanics of hearing ; giv- 
ing a full description of the ear, its 
structure, and the functions of its several 
parts. The Helmholtz theory is developed 
with relation to recent work, and the re- 
action of the nerves in transmitting audi- 
tory stimuli is explained. 

The "threshold of audibility" and the 
"threshold of feeling," together with other 
factors governing the limits of hearing, 
such as feeling intensity and pitch are 
treated in chapter two. 

The applications of the Weber-Fechner 
law and the determination of minimum 
perceptable differences in sound are studied 
in chapter three. In this connection the 
work of such experimenters as Knudsen, 
Riesz, Wegel, and Lane has been reviewed. 

Chapter four treats of the masking of 
sounds — one by another, taking up in this 
respect pure tones, subjective tones, com- 
plex sounds, and the calculation of the 
form of vibration of the basilar membrane. 
The masking of sounds is a phenomenon 
long known to physicists, but which has 
been accurately measured for the first time 
in Bell Telephone Laboratories. 

Binaural phenomena, including complex 
sounds, binaural beats, and sound images 
are taken up in chapter five. 

In chapter six are explained the various 
tests used in determining the acuity of 

hearing. This chapter also offers a de- 
scription of the audiometer, an instrument 
for the measurement of hearing, developed 
under the author's direction. 

A discussion of loudness, which covers 
loudness of sound, pure tones, complex 
sounds, the calculation of loudness losses, 
and the comparison of observed and calcu- 
lated values introduces the fourth section. 

Chapter two explains how the pitch of 
musical tones are recognized. 

Speech sounds and their recognition, in- 
telligibility tests, and probability applied to 
articulation are covered in chapter three. 

In chapter four the effects of change in 
intensity on the recognition of speech 
sounds are shown, together with a descrip- 
tion of the method and apparatus used. 

Chapter five shows how frequency distor- 
tion affects the recognition of speech 
sounds, and describes the performance of 
tests that indicate the importance of fre- 
quencies in recognizing sounds. 

In the sixth chapter the influence of 
other types of distortion on the recogni- 
tion of speech sounds are pointed out. 
Those considered are : the "overload" on 
the vacuum tubes in amateur radio receiv- 
ing equipment, reverberating qualities of 
rooms, the variance in speed between a 
phonograph turntable and the turntable 
used for producing a given record, and the 
difference in the frequency of sending and 
receiving carriers in carrier telephone 

Chapter seven is given to noise and deaf- 
ness and their effects upon the recognition 
of speech sounds. Experiments and discus- 
sions are included that are explanatory and 
descriptive of these relations. 

The book is brought to a close by five 
appendices : the first of which relates to 
the calibration of a condenser transmitter 
through the use of a thermophone ; the sec- 
ond to the derivation of equation relating 
to the properties of a plane wave ; the third 
applies Hook's law to the transmission 
of sound in the inner ear : the fourth es- 
tablishes the mathematical relation between 
hearing loss and the maximum distance for 
hearing and understanding speech ; the fifth 
gives a method for computing the loudness 
loss with a known characteristic impedance, 
and the sixth relates to the mathematical 
determination of the velocity in singly- 
resonant systems. 

Projection Engineering, September, 1929 

Page 29 

Tinted Films for Sound Positives 

The Problems Revolving Around the Use of Color in Connection With 
Film Having a Sound Track 

By Loyd A. Jones* 

POSITIVE motion picture film on 
tinted support lias been available 
for many years. It has been used 
extensively ; in fact during some 
periods within the past few years 
eighty to ninety per cent of the total 
production has been printed on tinted 
positive film. There is little doubt that 
the employment of material which im- 
parts a pleasing and variable color to 
the screen adds to the beauty of the 
production, breaks the monotony of 
looking for lone - periods at a plain 
black and white picture, and softens 
harsh outlines which otherwise may 
produce unpleasant impressions. But 
of much greater importance than these 
rather incidental esthetic contributions 
of color is its great potential power to 
enhance, by either objective or subjec- 
tive association, the emotional signifi- 
cance of the scene with which it is as- 
sociated. It must be admitted that the 
language of color — the more or less 
precise evaluation of the emotional 
value of the various hues, tints, and 
shades — is at present in a very rudi- 
mentary stage of evolution. Correla- 
tions are in many cases subconsciously 
felt without being consciously defined. 
It is entirely possible, and in fact prob- 
able, that careful study and experi- 
mentation may lead to the development 
of this language or symbolism into a 
powerful emotional tool in the hands 
of the master motion picture dramat- 

Recent scientific advances have made 
possible the reproduction of sound 
along with the motion picture, the 
sound record, consisting of a series of 
photographic images varying in either 
density or width, being carried on the 
edge of the positive film band. Al- 
though this has ndded enormous possi- 
bilities to the dramatic power of the 
motion picture, it has made it impossi- 
ble to continue the use of the tinted 
positive films which have been em- 
ployed during past years. Tin 1 re- 
corded sound is reproduced by the ac- 
tion of light which passes through the 

record on the positive film and excites 
a photoelectric cell. The majority of 

dyes used in making those tinted liases 

absorb strongly those wavelengths of 
radiation to which the photoelectric 

cell is most sensitive. Hence the re- 
sponse of the cell is so reilueed in mag 

oitude that high amplification of the 
photoelectric currents Is required to 

obtain SUffiCienl volume of sound. This 

high amplification may Increase unduly 

the inherent cell noises and micro- 
phonic disturbances in the amplifier 80 

that the reproduced sound is of intoler- 
ably poor quality. As a result, the use 
of tinted film has been entirely discon- 
tinued in the production of positives 
carrying a photographic sound record. 
There is little doubt that this absence 
of color from the screen constitutes a 
serious impairment of the beauty and 
dramatic power of the screen produc- 
tion. It is desirable, therefore, that a 
means be found for producing a tinted 
positive film which, when used in mak- 
ing sound positives, will not interfere 
with the satisfactory reproduction of 
the sound record carried thereon. 

All-over Tints vs. Clear Sound 

This problem can be solved provided 
coloring materials can be found which, 
while absorbing a relatively small 
amount of that radiation to which the 
photoelectric cell is most sensitive, will 
produce, by selectively absorbing the 
radiation to which the eye is sensitive, 
colors or tints of the desired hue and 
brilliance. These dyes, or carefully de- 
termined combinations of dyes, can be 
applied to the film base in the usual 
manner and thus enable the manufac- 
turer to offer a product at no greater 
cost than the regidar clear base posi- 
tive film. 

Another solution of the problem lies 
in applying the tinting dyes to the film 
band in such a manner as to leave un- 
tinted a narrow strip of proper dimen- 
sions and position on the film band. 
The sound record can then be printed 
on this uncolored area and the sound 
will be satisfactorily reproduced with- 
out interference of the tinting material. 
Unfortunately (his method involves a 
greater cost of manufacture, since the 

tinting dyes must be applied to the in- 
dividual 35 mm. strip after the base 

has been emulsion coaled and cut into 
DarrOW widths. It is obvious thai 

technically this represents the most 

satisfactory solution. This was reCOfi 

lllllll tiiiiinii 

Fig. 1. Spectrnl 
s ensitivity 
curves for (A) 
potassium qas- 
filled photoelec- 
tric cell and 
(B) caesium 
tric cell. 


nized by us some considerable time ago 
and applications were made for patents 
to cover the idea. Methods and ma- 
chines for accomplishing this have been 
devised which give very satisfactory re- 
sults and it is probable that this ma- 
terial will be available in the near fu- 

The first solution suggested, namely, 
the use of dyes or other coloring ma- 
terials applied over the entire area of 
the film and so adjusted spectrophoto- 
metrically as to transmit freely the 
radiation to which the photoelectric 
cell is sensitive, seemed worth further 
study, and after a rather lengthy series 
of experiments a number of satisfac- 
tory tints have been obtained. These 
represent the entire gamut of hue and, 
in our opinion, are of the most satis- 
factory depth or color saturation for 
use in applying color to the motion pic- 
ture screen. 

Color Sensitivity of Different 
Photoelectric Cells 

In approaching the problem of se- 
lecting dyes for this purpose it is nec- 
essary, first of all, to determine just 
what wavelengths of radiation most 
strongly excite the photoelectric cell 
with which the tinted material is to be 
used. It is necessary, therefore, to de- 
termine (he spectral sensitively of such 
cells. Photoelectric cells may be made 
by using any one of several different 
materials, such as potassium, caesium, 
sodium, and other alkali metals. These 
may be of either the evacuated or the 
gas-tilled type. The spectral sensitivity 
depends upon many factors and as a 
result cells differing enormously in 

spectral sensitivity are available. To 
the best of our knowledge, how- 
ever, there are only two types of 
cells used extensively in commercial 
Installations for the photographic re- 
production of sound. Qne of these. 
manufactured by the Western Electric 
Company and used in the equipment 

: Presented at thr Man. l!>2a mei 
of thr Snrirtu of Motion Picture Engineer! 

• Knrlnl; Research Laboratories. 

wo too 

WAVC UJiGTH (rnfi.) 

Page SO 

Projection Engineering, September, 1929 


Fig. 2. Visibility 
and tungsten 
energy 3000 C K: 

(A) relative 
energy of radia- 
tion from tung- 
sten at 3000° K; 

(B) visibility of 
radiation (rela- 
tive bright- 
nesses for equal 


500 fcDO 


installed by the Electrical Research 
Products Incorporated, is of the 
potassium gas-filled type. The other, 
used in the equipment installed by the 
Radio Corporation of America, is of 
the caesium type. 

In Fig. 1 are shown the spectral 
sentitivity curves of these two cells, 
curve A being that for a potassium and 
curve B that for a caesium cell. The 
ordinates of these curves are propor- 
tional to the photoelectric currents 
generated when excited by equal 
amounts of energy of the wavelength 
as indicated by the abscissa values. 
The proportionality constant used in 
plotting these curves is not the same 
for the two cells ; hence these curves 
cannot be interpreted as indicative 
of the relative total sensitivities of the 
two cells. They do show, however, the 
way in which sensitivity varies with 
wavelength, and this is the informa- 
tion in which we are particularly inter- 
ested at present. The monochromatic 
radiation used in the determination of 
these sensitivity functions was of high 
spectral purity, being obtained by using 
two monochromatic illuminators oper- 
ated in tandem so as to effectively 
eliminate all scattered radiation. The 
photoelectric current generated was 
measured with a high-sensitivity gal- 
vanometer. The amount of energy inci- 
dent upon the photoelectric cell was 
measured by means of the thermopile 
and high-sensitivity galvanometer. 
Since the thermoelectric current is 
directly proportional to the energy 
incident upon the thermopile (regard- 
less of wavelength) it follows that the 
sensitivity of the photoelectric cell, 
defined in terms of the photoelectric 
current per unit of energy, is directly 
proportional to the ratio of the photo- 
electric current to the thermoelectric 
current, Pc/Tc Every precaution was 
taken to eliminate all possible errors 
and it is felt that the curves shown in 
Fig. 1 represent with high precision the 
sensitivity of the cells in question. 
The author is indebted to Dr. Otto 
Sandvik of these laboratories for these 

The curves in Fig. 1 show the rela- 
tive magnitude of the photoelectric 
currents resulting from the action of 
equal amounts of energy of different 
wavelengths. In practice, the photo- 
electric cell is excited by an incan- 

descent tungsten lamp which does not 
emit equal amounts of energy at all 
wavelengths. To obtain the effective 
spectral response curve it is necessary 
to know the spectral distribution of 
energy in the radiation emitted by the 
incandescent tungsten lamp. This de- 
pends upon the temperature at which 
the filament is operated. In commer- 
cial sound reproducing installations 
this is approximately 3000°K. In Fig. 
2, curve A shows the relative intensity 
of the radiation ejinitted at different 
wavelengths for this source. It will 
be noted that relatively little energy 
is emitted in the short wavelength 
region to which the photoelectric cells 
are most sensitive, while relatively 
large amounts of radiation are emitted 
at longer wavelengths. 

In Fig. 3 are shown the effective 
spectral response curves for each of 
the two cells when used with a tung- 
sten lamp operating at 3000°K. The 
ordinates of these curves are deter- 
mined by multiplying, at each wave- 
length, the ordinate of the sensitivity 
curve (see Fig. 1) by that of the tung- 
sten energy curve, Fig. 2. 

It will be noted that the response 
curve of the potassium cell (A, Fig. 
3) has a relatively high sharp maxi- 
mum at wavelength 425 m/*. It de- 
creases rapidly for both longer and 
shorter wavelengths, reaching a value 
of 10 per cent of the maximum at 490 
mu., on the one hand and 340 mu. 
(estimated) on the other. The effect- 
ive response curve for the caesium cell 
is shown in Fig. 3, curve B, and is of 
a broad flat type having a maximum at 
420 mu.. For longer wavelengths the 
response decreases gradually reaching 
a value which is 10 per cent of the 
maximum at approximately 750 ma. 
The response at 700 mu., the long wave- 
length limit of the visible spectrum, is 
35 per cent of that at the maximum. 
It will be noted that the maximum of 
response is at practically the same 
wavelength for these two cells, 
although the caesium cell has a much 
broader spectral sensitivity than the 
potassium cell. It is evident from a 
consideration of these response curves 
that any coloring material which ab- 
sorbs strongly in the region between 
400 and 500 mu. will have a relatively 
high density if measured in terms of 
this photoelectric cell and a tungsten 

lamp. These wavelengths impinging 
on the retina give rise to the colors 
described qualitatively as violets and 
blues, and if these wavelengths are 
absorbed from white light the re- 
mainder produces a yellow color. 
Yellow dyes in general therefore have 
high photoelectric densities. This is 
true qualitatively for both cells al- 
though it applies with much greater 
force in case of the potassium cell 
which has a relatively narrow sensi- 
tivity band in the short-wave region. 
As a result of the difference in shape 
of the response curves, certain colors, 
such as yellows, give relatively lower 
photoelectric densities when measured 
with the caesium cell than when this 
quantity is determined by means of 
the potassium cell. 

Color Sensitivity of the Eye 

The eye is a receptor of the syn- 
thetic type and does not analyze a 
heterogeneous radiation into its com- 
ponent parts. The sensation arising 
from the impingement of heterogeneous 
radiation on the retina has a single 
hue characteristic, and identical sen- 
sations of hue may be excited by 
heterogenous radiations differing very 
widely in actual spectral compositions 
as determined spectrophotometrically. 
It is evident, therefore, that there is 
a possibility of obtaining a desired 
color by several different types of 
spectral absorption curves. Since the 
radiation required to actuate the 
photoelectric cell is localized in a very 
definite wavelength region, it follows 
that the course to be pursued in the 
solution of the problem in hand is to 
select absorbing materials which most 
efficiently transmit these wavelengths 
and at the same time most completely 
absorb those wavelengths which, when 
subtracted from white light, operate 
most efficiently toward the production 
of a color having the desired hue and 
saturation characteristics. 

In order to proceed most directly 
and logically in this direction, knowl- 
edge of the visibility of radiation is of 
considerable importance. This knowl- 
edge is of assistance in deciding just 
what particular type of selective ab- 
sorption will most efficiently produce 
a desired color and, at the same time, 
most efficiently transmit those wave- 
lengths which are required to excite a 
photoelectric cell. Curve B in Fig. 
2 shows this visibility function, the 
ordinates being proportional to the 
magnitude of the visual sensation pro- 
duced by the action on the retina of 
equal intensity of radiation of the 
various wavelengths, as indicated by 
the abscissa values. 

By judicious choice of dyes and 
dye mixtures which give spectral ab- 
sorptions correctly adjusted with 
respect to the photoelectric response 
and to the retinal sensitivity, it has 
been found possible to produce a series 
of colors having hues distributed 
throughout the entire hue scale and at 
the same time having relatively low 
densities as measured with either the 

Projection Engineering, September, 1929 

Page 31 

potassium or the caesium photoelectric 
cell-tungsten lamp (3000°K) combina- 

As a preliminary to this work a care- 
ful spectrophotometric analysis show- 
ing the selective absorption character- 
istics of several hundred available 
dyes was made. It was soon found 
that it would be quite impossible to 
produce colors of the red-orange- 
yellow group without absorbing some 
of the radiation to which these photo- 
electric cells are most sensitive. The 
question than arose as to the absorp- 
tion permissible in practice. There are 
really two phases to this particular 
problem, one involving a determination 
or decision as to the magnitude of 
photoelectric absorption for which 
satisfactory compensation can be made 
by increasing amplification without 
encountering serious electrical diffi- 
culties or sacrifice of quality in the re- 
produced sound. The other involves 
a consideration of the volume change 
which takes place in passing from one 
color to another when these are 
assembled consecutively in a reel of 
sound positive. 

Permissible Range of Photoelec- 
tric Density of Tints 

A large number of experiments were 
made in this laboratory to gather in- 
formation upon which a rational de- 
cision relative to these points could be 
made. After having reached con- 
clusions as to satisfactory values for 
maximum and minimum photoelectric 
density values, the matter was dis- 
cussed with several authorities in the 
field of photographic sound reproduc- 
tion, communicating engineering and 
acoustics. The opinions from these 
individuals corresponded surprisingly 
well with those based upon our experi- 
mental results. There seems to be no 
difficulty encountered in increasing 
amplification to compensate a photo- 
electric density of 0.3. This photo- 
electric density can be looked upon as 
equivalent to a certain loss of volume 
which in turn can be expressed in 
terms of transmission units (decibels). 
In order to convert a density value, 
density being defined as the logarithm 
of the reciprocal of transmission, to 
equivalent decibels it is only necessary 
to multiply by 20. Thus, if an optical 
density of 0.3 (measured, of course, in 
terms of the photoelectric cell and 
tungsten lamp combination being used i 
be inserted between the exciting lamp 
and the photoelectric cell it will be 
necessary to increase the amplification 
by 6 decibels in order to obtain the 

same volume output. On commercial 
equipment the volume control is ad- 
justable by steps, in some cases each 
step corresponding to 2 decibels, and 
in others to 3 decibels. Thus, the use 
of a tinted film base having a densitj 
of 0.3 will necessitate advancing the 
volume control by either 2 or '■'■ Steps, 
This represents a relatively small per- 
centage of the total amplification, and 
there seems to be little doubt that the 

required increase in amplification can 
be obtained satisfactorily. 

Permissible Volume Changes 

The permissible change in volume 
occurring in passing from one tint to 
another is, in the last analysis, de- 
pendent upon the sensitivity of the 
ear to changes in volume. Under ideal 
conditions of observation, the change 
in loudness corresponding to a volume 
change produced by one decibel varia- 
tion in amplification is just perceptible. 
It should be remembered that this 
change is perceptible only under ideal 
conditions. This situation is similar 
to that which exists relative to photo- 
metric sensitivity, that is, the sensi- 
tivity of the eye to differences in 
brightness. For instance, in a photo- 
metric field where the two halves are 
immediately juxtaposed in such a 
manner that when the two parts of a 
field are identical in brightness the 
division line is invisible, a difference 
in brightness of 2 per cent (actually 
1.7 per cent) is just perceptible pro- 
vided that the field subtends a visual 
angle of 3°, that the brightness level 
is optical, and that all disturbing fac- 
tors are removed. Such ideal con- 
ditions seldom exist in practical work, 
however, and it is customary to regard 
a brightness difference of 5 per cent as 
the least difference which is of im- 
portance. Similarly, in the case of oral 
sensitivity, when the comparison is 
made between pure tones of the same 
frequency immediately juxtaposed in 
time and of a loudness to which the 
ear is most sensitive, one decibel is 
just perceptible. In practice, however, 
it is probable that 2, or even 3 de- 
cibels constitutes a more rational 
specification of the amplification change 
which will produce a just noticeable 
difference in volume. On assuming, 
therefore, that a section of uncolored 
base is followed by a colored base 
having a photoelectric density of 0.3. 
the change in volume of 6 decibels will 
represent two, or perhaps three, just 
noticeable differences. Although this 
variation in most cases may not be 
unduly objectionable, it is felt that it 
is somewhat too great to meet the mosl 
rigid requirements. It is therefore 
proposed to establish also a lower 
density limit of 0.10 and to adjust the 
selective absorption of all the members 


Fig. 3. Effective 
response curves 
when using a 
tungsten lamp 
operating a t 

3000 K; (A) 
potassium cell; 
i B) caesium 

of the series so that none shall have a 
density less than this value. Further- 
more, it is proposed that when a hue- 
less screen is desired a positive film 
tinted with a neutral (non-selective) 
dye be used. The photoelectric and, 
incidentally, the visual density of this 
is adjusted to a value of 0.10 corre- 
sponding to 2.0 decibels. If this ma- 
terial is used in conjunction with one 
having a density of 0.3 the volume 
change occurring at the transition 
from one to the other will be that 
corresponding to a change in amplifica- 
tion of 4.0 decibels. This total change 
is a little greater than the volume 
change which under practical con- 
ditions is just noticeable, and is cer- 
tainly less than two such steps. It is 
felt that volume changes of this magni- 
tude are entirely negligible in prac- 
tical work, especially since a change 
from one tint to another usually 
occurs with a scene change at which 
point a slight volume change may 
logically be expected. 

It is of interest to apply this reason- 
ing also to the case of maximum per- 
missible density discussed in the 
previous paragraph. It will be re- 
called that a value of 0.3 for photo- 
electric density was fixed as being a 
reasonable upper limit. The amplifica- 
tion change required to give the same 
volume with such a film, as compared 
with clear base positive, is 6 decibels, 
which corresponds to two or perhaps 
three just noticeable volume differ- 
ences. It is evident that this repre- 
sents a relatively small increase in 
amplication and that no serious diffi- 
culty should be encountered in raising 
amplification sufficiently to compensate 
for the use of a colored base having a 
photoelectric density of 0.3. 

The conditions which have been 
established, relative to permissible 
photoelectric density of tinted base Cor 
use in making sound positives, may be 
summarized as follows: 

Maximum photoelectric density 0.3, 
amplification increment decibels. 

Minimum photoelectric density Old. 
amplification increment 2 decibels. 

Maximum variation in density 0.20, 
maximum volume variation 4 decibels. 
It shonld be understood that the 
values of density specified above are 
relative to clear film base taken as 

5 i» 


ii iiHiiiiiiiin 

I" \ ^^ 

soo wo 

WAVt LtKOTM(n\>«.) 

Page 32 

Projection Engineering, September, 1929 

Table I 



istics of the 

series of tints 


Color Name 







Clear base 



Hueless, clear 


Rose Doree 




Deep warm pink 






Flesh pink 






























































Fleur de lis 







-55 1 









Cool pink 











equivalent to a transmission of 100 
per cent, density 0. It seemed desir- 
able to express all results in this man- 
ner since the factors of interest are 
those relating to the changes of photo- 
electric transmission, volume, etc., as 
compared to the conditions existing 
when the sound record is carried on a 
clear film base. 

Visual Characteristics of the Seven- 
teen Tints 

In Table I are given data relative 
to the visual characteristics of these 
tinted materials. Considerable thought 
has been given to the names by which ' 
these tints are to be designated. It 
seems desirable, from a consideration 
of the probable associational and 
emotional value of color when applied 
to the motion picture screen, to desig- 
nate these tints by names suggestive 
of their potential psychological effects 
and appropriate uses. This particular 
phase of the subject will be discussed 
in greater detail in a later section of 
the paper. In the column designated 
as "i" under the title "Hue" are given 
the values of the dominant hue ex- 
pressed in wavelength. These deter- 
minations refer specifically to the color 
of a white screen when illuminated by 
light from an arc of the reflector type 
with the tinted base placed between 
the light source and the screen. It 
therefore is a specific designation of 
the screen color obtained when these 
materials are used with a light source 
of this character. It is realized that in 
practice a certain variation in these 
hue values will result from the use of 
light sources differing from the one 
with which these hue measurements 
were made. For instance, with a high 
intensity arc of either the condenser 
or the reflector type, the color of the 
emitted light is probably slightly bluer 
than that emitted by a reflector arc 
using ordinary hardcored carbons. 
Under these conditions the hue values 
will be shifted slightly. The differ- 
ence, however, is so little as to be con- 
sidered negligible from the practical 

standpoint. If these materials are used 
in a projector employing a high 
efficiency tungsten lamp there will 
probably be a rather great departure 
from the hue values indicated in Table 
I. This light is much yellower than 
that emitted by the arc and hence the 
use of a screen illuminated by a tung- 
sten lamp in conjunction with these 
tinted bases will give appreciably dif- 
ferent hues from those indicated in 
Table I. In the column designated as 
"No." under "Hue" are the Ridgway 
hue numbers. The system of color 
nomenclature developed by Ridgway 1 
is one of the best available. The entire 
hue gamut, including the spectral hues 
and the non-spectral purples, is divided 
in 72 hue steps. These hue steps are 
equally placed on the sensation scale. 

1 Ridcjivay. 
cloture, 1912. 

Color Standards and Nomen- 

Tints Evenly Spaced Along Normal 
Hue Scale 

In setting up a scale of hue it is not 
satisfactory to adopt intervals which 
are identical in wave-length difference 
because the sensitivity of the eye to 
hue differences varies enormously 
throughout the spectrum. In order to 
establish a normal hue scale in which 
the steps are equal in terms of ' sensa- 
tion, it is necessary, therefore, to use 
wave-length intervals differing widely 
in magnitude. It will be noted that, 
with the exception of a region in the 
orange, yellow, and yellow-green, the 
hues of these tinted materials are 
fairly evenly spaced on the normal 
hue scale. It seems highly desirable 
to adopt such spacing, since it makes 
available the entire gamut, of hue and 
a change from one tint to another pro- 
duces a hue displacement of known 
and fairly equivalent subjective mag- 
nitude. The positions of the dominant 
hues of these colors are shown graph- 
ically on the chart in Fig. 4. At the 
left are given the Ridgway hue num- 
bers and the names applied by Ridg- 
way to these hues when occurring in 
colors of high saturation. At the right 
in the first column are the Ridgway 
hue numbers for the tinted positive 
films, and the names applied to these. 
It should be remembered that these 
colors are in general of relatively low 
saturation and it is considered that 
these more delicate tints are of greater 
utility for use in applying color to the 
motion picture screen than those of 
higher saturation. It is a rather pe- 
culiar coincidence that the colors cor- 
responding to the hue numbers 25 to 
35, which are absent from this positive 
film series, are those which, according 
to all of the available psychological 
data (see Luckiesh, loc. cit.), are the 
colors classified as least agreeable or 
least preferred. These color preference 
data are derived from a large group 

Table II 


Photoelectric density characteristics of the 
Film Tint Potassium 

Clear base 0.0 





3 4 





5 6 

5 2 






2 2 
1 8 

3 6 
3 5 
3 8 

of tints 





Rose Doree 





. 17 

2 2 










1 8 








3 6 








4 8 




5 4 




5 6 




4 4 


Fleur de lis 

Amaranth . 




4 8 





2 8 
4 4 









3 7 
1 2 

Maximum A 


4 S 

Projection Engineering, September, 1929 

Page 33 

of observers and hence are very signi- 
ficant. It has been impossible thus far 
to obtain these hues with sufficiently 
low photoelectric density. Possibly 
further search may reveal dyes which 
will permit the manufacture of these 
hues if such seems to be necessary or 

In Table I, in the column designated 
as "T," are the values of total trans- 
mission for these colored materials as 
measured visually using the reflector 
arc as a light source. These values are 
therefore a direct measure of the 
screen brightness obtained when using 
these tinted materials as compared 
with the screen brightness existing 
when using clear base positive. It will 
be noted that the visual transmissions 
of the red, orange, yellow, and yellow- 
green colors are relatively high, while 
those of the green, blue, violet series 
are relatively low. This condition 
exists since it is desired to obtain 
fairly definite color saturation effects. 
It follows as a natural consequence of 
the visual sensitivity and transmission 
characteristics of dyes that the colors 
in the former group have relatively 
high visual transmissions for a speci- 
fied color saturation, while the trans- 
mission values in the second group 
are in general low when a correspond- 
ing color saturation is obtained. In 
the last column are given short verbal 
descriptions of the color character- 

To show spectrophotometry curves 
for all of the seventeen members of 
this series seems unnecesasry, but it 
may be of interest to consider two or 
three typical cases. In Fig. 5 are «iven 
such curves for tint No. 1 (Rose 
Doree), a warm deep pink; tint No. 8 
(Aquagreen), a clear blue-green; and 
tint No. 11 (Nocturne), a deep violet- 
blue. Inspection of the curves shows 
that each of these colors has a decided 
density minimum throughout all or 
some part of that wave-length region 
in which the photoelectric response is 
maximum. The minimum density does 
not fall at the same wave-length in 
each case but shifts with the demands 
of the selective absorption necessary 
for obtaining the desired visual hue. 
In Table II are given data relating 
to the photoelectric density charac- 
teristics of these materials for potas- 
sium and caesium cells of the types in 
extensive use in commercial installa- 
tions. Density values are designated 
as "D," while in the columns desig- 
nated as "Db." are given the equiva- 
lent values in decibels, these represent- 
ing the amplification increinenl re- 
quired to compensate Cor the volume 
depression occasioned by the ose of 
these materials. 

It will he noted that the specifica- 
tions relative to maximum density and 
maximum density difference previ- 
ously set forth as desirable nave been 
met in actual materials with a fair 
degree of precision. In case of the 
potassium cell the maximum density Is 
0.28 (No. 7, Verdante), slightly less 
than the value of 0.80 considered 






























































Fig. 4. Positions of the tints on the Ridgway Hue Scale. 

allowable, while the density differ- 
ence between the upper and lower 
Limits is 0.1!) (equivalent to 3.S deci- 
bels), also slightly less than that con- 
sidered tolerable. With the caesium 
cell the maximum density Is exactly 
0.30 (No. 13, Flour do lis), while the 
maximum difference Is 0.24, ool appre- 
ciably greater than the specified 0.20. 
The volume variation through the 

entire series of seventeen tints i< 

shown in Fig. 6. The ordinates Indi- 
cate the Increase In amplification ex- 
pressed in decibels required In each 

Cast to give the same volume oulpul 

with the tint as indicated by the cum- 
bers al the bottom of the figure, as 

C pared With a sound record of 

identical characteristics on the reg- 
ular clear positive film, The horizon- 
tal lines are drawn at plus and minus 
i' decibels from the mean' of the entire 
group. These lines therefore define 
the allowable volume change as previ 
oualy specified, in case of the pots 
slum cell all <>f the tints fail between 

these limits; with tl aeslum cell 

two of the tints fall slightly oul Ide 

these limits. 

Prints have been made on nil of 

these colored bases and sound repro- 

duction with each cell is considered 
satisfactory, both with respect to the 
increase in amplification required and 

the maximum volume variation. It is 

hoped thai the sound prints to be 

shown B little later will demonstrate 

this poinl to your satisfaction. 

This concludes thai part of the 

paper which may be designated as 
technical, dealing, as it does, with the 
objective or physical characteristics 
of tinted positive film base. The appli- 
cal Ion ol these colors to a mol ton pic- 
ture production Involves the considera- 
tion Of B radically different group of 
relationships belonging to that phase 
of the motion picture Industry which 
has been designated, tor want of 
heiier term, as artistry, w bile it may 
i>c presumptuous on the pari of the 
author <>f this paper to Invade a field 
bo remote from thai of bii accustomed 
activities, he feels thai there ma.\ be 
-'pine members of the Society more 
concerned with the artistic and emo- 
tional reactions than with the cold 
facis of scientific technology, who may 
be Inters ted I or perhap amused) by 
Borne thoughts and sugge ! Ion 

'Lovd i /one*. Trant, Soc Mol Plot 
/'iic Wo. 18 15. 19 

Page 34 

Projection Engineering, September, 192'J 

the possible emotional and artistic 
value of color applied to the motion 
picture screen. Some of you may have 
been present on one or two previous 
occasions when the author has had the 
privilege of presenting to this Society 
papers, written in collaboration with 
Townsend 3 and Tuttle 4 discussing the 
use of color in more or less abstract 
static and dynamic forms as a valu- 
able element in a motion picture pro- 
gram. You are already aware, there- 
fore, that he has long been interested 
in the possibilities of color as an aid 
to the creation of dramatic atmos- 
phere. In fact he is firmly convinced 
that color per se, if properly em- 
ployed may exert a powerful influence 
on the emotional reactions. He there- 
fore begs your indulgence while in 
the following pages a few ideas along 
these lines are presented for your 

The Language of Color 

The literature pertaining to the lan- 
guage, symbolism, and emotional 
effects of color, though scattered and 
fragmentary, extends over the entire 
period of recorded history. Mythology 
is replete with the symbolism of color. 
On the Greek stage the colors of the 
costumes were adjusted to the mood 
of the action. Color is intimately asso- 
ciated with the entire history of the 
Christian Church and a very definite 
color symbolism has developed. Color 
has been so inseparably linked with 
sensory experience throughout the evo- 
lution of mankind that it has acquired 
by objective and subjective association 
definite and important emotional 

No attempt can be made within the 
confines of this paper to give anything 
approaching a complete bibliography 
of the subject. One or two references, 
however, may be valuable to those in- 
terested. Field in his Chromatog- 
raphy* discusses various colors from 
the standpoint of their emotional value 

3 Loyd A. Jones and L. M. Toxensend. 
Trans. Soc. Mot. Pict. Eng. No. 21 :3S. 

4 Loyd A. Jones and Clifton Tuttle. 
Trans. Soc. Mot. Pict. Eng. No. 28 :183. 

5 George Field. Chromatography. Charles 
Tilt, 1835. 

and gives numerous references tend- 
ing to show rather general agreement 
as to the character of such effects. A 
quotation given by Field 8 from Opie, 7 
an English artist of the late 18th cen- 
tury, is of particular interest. 

"Every passion and affection of the 
mind has its appropriate tint and col- 
oring, which if properly adapted, lends 
its aid, with powerful effect, in the 
just discrimination and forcible ex- 
pression of them ; it heightens joy, 
warms love, inflames anger, deepens 
sadness, and adds coldness to the 
cheek of death itself." 

The most recent, complete, and by 
far the best publication on this sub- 
ject is that by Luckiesh. 8 This is 
a carefully considered conservative 
treatment in which are given numer- 
ous data 'collected from many fields 
along with the valuable contributions 
of the author to this subject. The book 
will repay careful study and is ear- 
nestly recommended to the attention 
of those interested. The following 
quotation" is of interest as it indicates 
the attitude of the author toward the 
subject and is an admirable statement 
of the point of view which should be 
taken by any investigator in a little 
known field. 

'"It would be unscientific to deny the 
existence of a language of color be- 
cause we do not understand it thor- 
oughly at present and quite unpro- 
gressive to reject the possibility of 
finally completing the dictionary of 
this language. Color experiences are 
indeed very intricate at present but it 
is likely that this is due to our scanty 
knowledge of the elements and proc- 
esses involved in the emotional appeal 
of colors, and to our inability to inter- 
pret and to correlate properly the vari- 
ous factors. Much knowledge must be 
unearthed before a rudimentary dic- 
tionary of this language is available 
but first the scientific attitude should 
admit the possibility that the language 
of the group of experiences associated 

°l. c. p. 11. 

' Opi^s Lecture IV, p. 147. 
8 Luckiesh. The Language of Color. 
Dodd, Mead and Company, 1920. 
9 1, c. p. 4. 

Fig. 5. Spec- 
trophotometr ic 
curves for Rose 
Doree, Aqua- 
green, and Noc- 

300 350 

450 500 550 


with color eventually will be under- 

In considering color from this point 
of view it must be remembered that 
we are now dealing with color as it 
appears, that is, the sensation evoked 
in consciousness, rather than with the 
objective character of color as deter- 
mined by its physical characteristics. 
All of the various factors, therefore, 
which determine the character of the 
subjective reactions, such as simulta- 
neous contrast, previous retinal excita- 
tion, and many others must be consid- 
ered in attempting to define the emo- 
tional reaction that may be induced by 
subjecting the eye to stimulation by 
radiation of known physical composi- 
tion. Moreover, a color may, just as a 
word or phrase, have more than one 
emotional value or significance; and, 
as in the case of the spoken language, 
the intended meaning must be deter- 
mined by the contextual factors such 
as general character of the scene 
structure, subject matter of preceding 
sequences, type of dramatic action, 
etc. For instance, a green matching 
in hue and saturation characteristics 
the color of spring foliage, may con- 
note by direct subjective association, 
springtime, trees, grass, gardens, etc. 
Used on radically different types of 
scenes, however, such as interiors, it 
may be found particularly valuable 
for suggesting by indirect or subjective 
association certain more abstract con- 
cepts, such as youth, freshness, hope, 
aspiration, and those moods closely 
linked in our consciousness with the 
springtime of life. 

Objective and Subjective Color 

A rather careful analysis of the ad- 
mittedly rudimentary color language 
indicates that the great majority of 
existing connotations may be classified 
in two rather distinct groups which 
may be designated as (a) direct ob- 
jective association and (o) indirect 
subjective association. It is relatively 
easy to quote many examples of the 
class a correlations. For instance, sun- 
light is quite definitely suggested by 
yellow. Now, as a matter of fact, 
sunlight is not yellow, and it has been 
shown definitely that when the retina 
is excited by sunlight or by radiation 
of identical spectral composition in a 
visual field from which all possible 
contrasting areas have been removed, 
the sensation evoked is hueless, that 
is, corresponding to gray or white. A 
white object, however, illuminated by 
sunlight under a clear blue sky ap- 
pears yellow. It seems quite evident, 
therefore, that through centuries of 
evolution a definite conscious or sub- 
conscious relationship between sun- 
light and yellow has been so estab- 
lished that under artificial conditions 
yellow almost invariably suggests sun- 
light. Thus a motion picture scene 
printed on yellow base, such as tint 
No. 6 (Sunshine), should definitely 
suggest sunlight illumination whether 
it be an exterior flooded with light 
from the sun or an interior into which 

Projection Engineering, September, 1929 

Page 35 

light is streaming through open doors 
or windows. 

In a similar manner there seems to 
be a very definite relationship between 
other colors and the well-known artifi- 
cial sources of heat and light. Artifi- 
cial illumination of interiors is defi- 
nitely suggested by a color which • is 
either more saturated or has a hue 
somewhat more orange than the yel- 
low suggesting sunlight. Firelight 
may be suggested by a color even more 
reddish in character. Such examples 
of objective association can be multi- 
plied almost indefinitely. Subjective 
associational relationships are some- 
what more tenuous and difficult to es- 
tablish with certainly. Some of these 
undoubtedly have been built up in con- 
sciousness by somewhat artificial asso- 
ciation of certain colors with definite 
emotional states. Others of these cor- 
relations may probably be traced to 
extensions of more direct associational 
factors. For instance, there seems to 
be a character of warmth associated 
with all of the colors in the yellow, 
orange, red, magenta category, while 
the remainder give a definite impres- 
sion of cold or coolness. This is very 
probably an extension of the more 
direct associational value arising from 
the color of sunlight and fire and the 
atmospheric conditions normally asso- 
ciated with coldness. The association 
of color with certain temperamental 
phases of life, such as youth, maturity, 
old age, etc., can probably be traced to 
an extension of a more direct associa- 
tion with the seasons of the year. 
Space does not permit us to carry this 
analysis into greater detail, but a 
serious study of the subject can hardly 
fail to convince the fair-minded stu- 
dent that there is really some definite 
and psychologically sound relation- 
ships between colors and emotional 
states. Although a great deal of the 
work on this subject has been of 
purely qualitative, and perhaps tem- 
peramental type, there are available 
some rather definite and significant 
data. For instance, Luckiesh 10 (loc. 
cit. p. 200) gives some very interesting 
data compiled by Wells' 1 relative to 
The general types or mood reactions 
produced by twelve different colors. 

"• I. o. r>- 4. 

a N. A. Wells. Psych. Bui. 7:181, 1910. 

. .. , 

Fig. 6. Volume 
variat ion r e - 
suiting from the 
use of the se. 
ries of seven- 
teen tints. 

a 2. 


C. K 




These data are shown in Table III. 
They are derived from sixty-three sub- 
jects and the correlation is indeed 
striking. There seems to be no escape 
from the conclusion that those colors 
designated as yellow, orange-yellow, 
deep orange, scarlet, and crimson have 
a definitely exciting influence. In the 
mid-spectrum yellow-green, green, and 
blue-green, seem to be definitely tran- 
quilizing or soothing. Blue, violet- 
blue, violet, and purple are depressive 
or subduing. The student who ap- 
proaches this subject with an open 
mind and with the intention of seri- 
ously searching for correlation factors 
can scarcely fail to be convinced that 
here is something of a very tangible 
nature which can be ascribed to a defi- 
nite psychological reaction to color. 

The chart in Fig. 7 shows the effec- 
tive values of the various colors as 
computed from Wells' data. No defi- 
nite information is available relative 
to the dominant wave-length of the 
colors used by him so they are plotted 
arbitrarily at equal intervals along 
the base line. The ordinates are com- 
puted from the data in Table III, 
each number being reduced to a per- 
centage of the total number of deci- 
sions. The curves have the following 
significance: (A) curve of exciting in- 
fluence; (B) curve of tranquilizing 
Influence; (C) curve of subduing 

Table III 

Wills' ilatii on tin affective values of various colors 

Total Number of Replies from 83 Subjects Indicating Three General Types 

of Mood-Reactions Due to the Twelve Different Colors. 

Exciting Tranqwilizing Subduing 

Influence Influence Influence 

Crimson " 10 

Scarlel 56 

l >eep orange • • • 59 " " 

Orange-yellow 55 

Yellow 53 6 

Yellow-green I I :;!l 5 

Green 28 -".2 

Blue-green 32 23 •'> 

Blue . II 21 80 

Violet-blue . 17 45 

Violet 6 54 

Purple . •"- ' 18 

7 a a io n is is i<v is is n 

These curves are suprisingly similar 
in general shape and position to the 
three fundamental retinal excitation 
curves for red, green, and blue-violet. 
Although the present data are too 
meagre to establish any correlation 
between emotional effect and the re- 
tinal processes, the similarity is cer- 
tainly sufficient to encourage some 
further consideration. 

Along the top line of the chart are 
placed the numbers referring to the 
positive film tints, the position of each 
relative to the color scale at the bot- 
tom being determined as carefully as 
the qualitative data will allow. The 
dotted lines dropped from these points 
cut the three curves and the heights 
of these ordinates give some idea of 
the character and strength of the 
mood reaction which each color may 
be expected to induce. 

In the upper part of the chart is 
drawn a curve showing in a qualita- 
tive way the position on the warm- 
cool mood reaction scale. This, it 
must be confessed, is based on very 
insufficient evidence, being determined 
by the rather casual judgments by a 
few observers working under poorly 
controlled conditions. 

Characterizations of the Seventeen 


In the following paragraphs an at- 
tempt has been made to give a brief 
description of the visual and psycho- 
logical characteristics of the film tints. 
It is evident that no very definite 
statements can be made or rigid speci- 
fications set up for the use of these 
colors, it is hoped that these rather 
disconnected and rambling remarks 
relative to the various colors may be 
of Interest to those concerned with 
working oul the application of color 
to the motion picture screen and serve 
as a foundation, however Insecure, 
upon which something of real value 
may be buill by others more Qualified 
by training and temperament for such 
work. Although these characteriza- 
tions of the symbolic and emotional 
values of these colors are necessarily 

tinged by the author's own reactions 

nmi by the results of his own Intros- 
pective analysis, they are based, in so 

Page 36 

Projection Engineering, September, 1929 

Fig. 7. Affective 
values of the 
various colors 
computed from 
Table III: (A) 
curve of excit- 
ing influence; 
it) curve of 
tranquilizing in- 
fl u e n c e ; (C) 
curve of subdu- 
ing influence. 

far as is possible, upon a careful sum- 
mary and integration of data derived 
from the available literature. They 
should therefore represent approxi- 
mately the reactions to be expected 
from the average observer. 

Tint No. 17. Argent. This is a hue- 
less color, a silvery gray showing no 
chromatic characteristics. It may be 
regarded as the zero or starting point 
on the scale of saturation or color 
strength. It is very necessary as a 
means of establishing a visual accom- 
modation in terms of which a hue may 
be appreciated by contrast. It may be 
used to fatigue the eye to the point 
of monotony, after which the presen- 
tation of hue will have enhanced 

Tint No. 6. Sunshine. A clear 
brilliant yellow approximately com- 
plementary to sky-blue, therefore 
quite closely matching the subjective 
color of sunlight when seen in con- 
trast to blue sky. The visual trans- 
mission is high (83 per cent) ; there- 
fore it is particularly adapted for use 
on a scene designed to give the im- 
pression of brilliant sunlit conditions 
and where an interior is obviously 
illuminated by sunlight entering 
through windows and open doors. 
This color is definitely warm but not 
to the same extent as Candlefiame, 
Firelight, and Afterglow which make 
with this color a series increasing 
progressively in warmth. It is mildly 
stimulating, suggesting a mood of 
lively interest and attention, but, not 
one of high excitment or nervous 

Tint No. 5, Candlefiame. A pastel 
orange-yellow. It is slightly lower in 
transmission (75 per cent) than Sun- 
shine, giving a screen more orange 
in hue and lower in brilliance which 
definitely suggests artificial illumina- 
tion when used on interior scenes. 
Somewhat warmer than No. 6. Possi- 
bly useful on exteriors in suggesting 
morning or afternoon with less intense 
sunlight than prevails at midday. By 
objective association useful in induc- 
ing rather mild mood reactions such 
as feelings of coziness, comfort, inti- 
macy, well being, peace and plenty 
without opulence, etc. 

Tint No. Jf, Firelight. A soft yel- 
low-orange. This is warmer than 
Candlefiame to which it is closely 
akin in mood reaction value. The 
lower transmission (66 per cent) 
gives a somewhat less brilliant screen 
and this with the more orange hue 
makes it particularly adapted for use 
on an interior scene where it is de- 
sired to suggest an artificial illumina- 
tion softened and subdued perhaps by 
shaded lamps and candles. It is sug- 
gestive also of illumination emanat- 
ing from an open fire ; but it is not 
quite orange or red enough to satis- 
factorily render the fire itself if 
visible, for which Afterglow is per- 
haps better. It stimulates mood re- 
actions of the same category as 
Candlefiame but with greater intensity. 
Suggestive of warmth, comfort, in- 
timate home relationships, mild affec- 
tion, etc. 

Tint No. 3. Afterglow. A soft rich 
orange color. It is probably the 
warmest color of the series. It is 
appropriate to exterior scenes at 
dawn and sunset. It lends to in- 
teriors an atmosphere of warmth and 
intimacy stronger than Firelight. It 
should excite mood reactions in general 
connected with luxury, wealth, secur- 
ity, and relatively strong affections. It 
is also related to the autumnal mood 
by obvious direct association with the 
autumn colors of nature. By indirect 
or subjective association it is symbolic 
of the same relative period in the life 
of an individual and its associated 
moods. It is indicative, therefore, of 
repose, ambitions attained, accom- 
plishment, and similar psychological 
aspects of maturity. 

Tint No. 2. Peachblow. A delicate 
flesh pink. This has a small but 
definite blue content, making it some- 
what less warm than Afterglow. It 
is adapted to the rendition of close- 
ups where it is desired to do full 
justice to feminine beauty. The hue 
and saturation are such as to suggest 
the glow of life. 

Tint No. 1, Rose Dore'e. A deep 
warm pink suggesting sensuousness 
and passion. Amorous, romantic, and 
exotic. It is adapted to the rendition 

of scenes representing an intimate at- 
mosphere, such as a luxuriously ap- 
pointed boudoir. In keeping also with 
feeling of happiness, joy, and excite- 

Tint No. 7, Verdante. A pure green, 
rather pastel in character. It is the 
hue of spring foliage, suggesting 
directly, trees, grass, and vernal land- 
scapes. By subjective association 
typical of youth, freshness, unsophisti- 
cation, innocence, etc. It is only 
slightly warm, but definitely not cold. 
It is very close to the neutral point 
in the warm-cool scale. 

Tvnt No. 8, Aquagreen. A brilliant 
blue-green. The color of more north- 
ern waters and suitable to the rendi- 
tion of the sea under clouds and in 
storm. It is suggestive of wetness. 
Its transmission (40 per cent) being 
lower than that of Verdante, it gives 
a less brilliant screen. This together 
with its greater blue tint probably 
makes it more suitable for the rendi- 
tion of the darker green of mature 
summer, foliage, dense forests of pine, 
jungles, etc. By extension from the 
objective correlation to summer it is 
suggestive of such mood reactions as 
pertain to maturity, wisdom, dignity, 
repose, and restfulness. It is cool but 
not cold ; tranquil, but not subduing. 
Tint No. 9, Turquoise. A clear 
brilliant blue. It is definitely cool, 
but less cold than Azure or Nocturne. 
The visual transmission (43 per cent) 
is high for a blue of this hue but 
low as compared to the warm colors. 
This gives a screen of depressed 
brightness which together with the 
hue tends to produce a mood of peace, 
reposefulness, and tranquility. It is 
the color of calm tropical seas under 
clear skies. It is suggestive of the 
Mediterranean and the South Sea 
Islands. If used on interiors it should 
impart a feeling of restfulness, 
dignity, and reserve without inducing 
appreciable depressive moods. With 
proper contextual influence it might 
be used for the suggestion of brilliant 
moonlight effects, although No. 10 
may be somewhat better for this 

Tint No. 10, Azure. A strong sky- 
blue. It is colder than Turquoise ; 
tranquilizing to the point of becoming 
depressing. The visual transmission 
(28 per cent) is relatively low and 
hence gives a screen of low brightness. 
It is suggestive of the sedate and the 
reserved, even approaching the aus- 
tere or forbidding ; under certain con- 
ditions slightly gloomy. 

Tint No. 11. Nocturne. Deep violet- 
blue. The visual transmission is low 
(28 per cent) giving a screen of low 
brightness. It definitely suggests 
night, shadows, gloom, coldness, etc. 
By subjective associational reactions 
appropriate to depressive conditions, 
despair, failure, unattained ambitions, 
intrigue, the underworld. 

Tint No. 12, Purplehaze. A bluish, 
violet or lavender, rather pastel in 
character. It has a relatively high 
visual transmission (40 per cent) giv- 

Projection Engineering, September, 1929 

rage 37 

ing a screen of greater brilliance, 
higher key, than the adjacent tints, 
Nocturne and Fleur-de-lis, to both of 
which it is closely related in emotional 
value. The mood induced by this 
color is particularly dependent (more 
so than many of the other colors) 
upon contextual factors. For in- 
stance, to a twilight scene on the 
desert with distant mountains it im- 
parts a feeling of distance, mystery, 
repose, and languorous warmth ; used 
on a scene containing snow fields, 
glaciers, snow-capped mountains, etc., 
it has a pronounced cooling effect. 
The hue of this color is approximately 
the same as that of the shadows on 
sunlit snow under a clear blue sky. 

Tint No. 13, Fleur-de-lis. A rich 
royal purple. This color has long 
been the badge of royalty, high office, 
power, and pomp. In ancient times 
the dye was very costly and was used 
to color the garments of the aristoc- 
racy. The transmission of this film 
tint is low (25 per cent), thus giving 
a depressed screen brightness sugges- 
tive of reserve, dignity, and austerity. 
It has a relatively cool color but not 
as cold as Nocturne. 

Tint No. 14, Amaranth. This is also 
a purple but has a greater red content 
than Fleur-de-lis ; therefore it is 
warmer and less austere. It is 
adapted to the rendition of scenes 
showing opulence and luxury together 
with refinement. With proper con- 
textual relation it may be well adapted 
to scenes approaching sensuality and 
abandon, such as bacchanalian revels 
staged in settings of wealth, and 

Tint No. 15, Caprice. Cool pink. 
Visual transmission (53 per cent) rel- 
atively high, thus giving a brilliant 
sparkling screen. It is a jolly, care- 

free, hilarious color suggestive of 
carnivals, Mardis gras, fete days, 
and merry making in general. 

Tint No. 16, Inferno. Fiery red 
tinged with magenta. Since it is 
directly suggestive of fire, it is 
adapted to scenes of burning build- 
ings glowing furnaces, forest fires, 
etc. By subjective association indica- 
tive of riot, panic, anarchy, mobs, 
turmoil, strife, war, battle, and un- 
restrained passion. 

Proper Use of Color on the Screen 

It is not desired that the reader 
shall gain the impression from this 
rather enthusiastic discussion of the 
potential emotional value of color that 
the lavish and unrestrained use of 
color treatments is advocated. On 
the contrary, it is desired to empha- 
size the necessity of using the color 
accompaniment to a motion picture 
production with care and discretion. 
The use of too strong or saturated 
colors is in general not good, since 
such colors are usually obstructive 
and distracting and may defeat rather 
than promote the attainment of the 
desired effect. A more subtle method 
will yield better results. This in- 
volves the employment of pastel tints 
which may be increased in subjective 
strength for a brief period of time by 
the action of successional contrast or 
juxtaposition in time. Thus the eye 
accommodated to, or fatigued by a 
green, such as Verdante, will per- 
ceive, at the beginning of the follow- 
ing scene done on a pink tint, a color 
of enhanced subjective saturation. 
This immediately fixes the mood of 
the scene, after which the accom- 
modational processes in the retina be- 
gin to operate and cause the effective 

saturation to decrease appreciably. 
Thus the color having fulfilled its 
mission, saying definitely that this 
scene has a specific emotional atmos- 
phere, fades into the background and 
while continuing to make itself felt 
in the subconscious mind of the ob- 
server by lending a warmth and soft- 
ness to the scene permits the action 
to carry forward the dramatic 
sequence without the unpleasant and 
distracting influence of pronounced 

There are perhaps some who may 
question the advisability of attempt- 
ing to use color on the screen as an 
aid to the creation of an emotional 
atmosphere on the ground that indi- 
viduals react differently to the same 
color. Is it not true that the same 
musical composition may excite dif- 
ferent feelings in individuals, and that 
the same word or phrase may convey 
to different minds somewhat diverg- 
ent ideas? Perhaps it will be neces- 
sary to spend much time and effort 
on the development of a language of 
color, to compile dictionaries with 
definitions of the symbolical, associa- 
tive, and emotional values, just as 
we write and agree upon definitions 
of words in order that specific ideas 
may be conveyed from one mind to 
another by spoken and_ written lan- 
guage. If there is in the human mind, 
or, more specifically, in the collective 
mind of the motion picture public, a 
color consciousness, even though it be 
at present latent or but slightly devel- 
oped, is it not worth considerable ef- 
fort in thought and experimentation 
to develop technique such that color 
can be applied to the screen in such 
a way as to enhance the emotional 
and dramatic values of the motion 
picture of the future? 

Tailor-Made Sound-Reproducing Systems 

THE average moving picture 
theatre owner seems to believe 
thai it is simply a matter of 
'Send me up a sound outfit," 
and his troubles are over. Far from it 
— they are just beginning. 

We were recently called upon to as- 
sist a figurative "stylish stout" in 
upper New York State, whose require- 
ments were delicate in the extreme. 
This particular theatre was aflli<-t <■<! 
with dead spots or areas, not neces- 
sarily far from the sound source, 
where practically nothing could be 
boa ril. Farther back In the theatre, 

reception was excellent, as il was to 

the and sides. The trouble was 
diagnosed in this case as conflicting 
BOUUd waves. A train of sound waves 
coming directly from the Btage, en- 
countered another train of waves de- 
flected straight down from the celling. 
Where the two met. they counteracted 
or neutralized each other to such an 

• Vice-President, itaiUn Receptor Co. 

By Ludwig Arnson* 

extent that practically nothing could 
be distinguished. The remedy in this 
case was found in the medium of dis- 
tribution, that is to say, in the use of 
directional speakers. The usual cone 
speakers were discarded and a num- 
ber of specially designed horns were 
substituted. Those horns, equipped 
with the best obtainable reproducer 

Hints, were placed at different angles 
and their relative positions varied 

until the ideal degree of reproduction 
was achieved, in this way we actually 
made the sound waves behave, direct- 
ing them the way wo wanted, to over 

come the natural defects of the 

tlieal re. 

Too Much Power 
Another effect encountered in some 

theatres is not so much a problem as 
an adv. -ml am-. althOUgb it may cost the 
owner just as much in the long run. 

We know, and the informed manager 
knows, approximately what quantity 

of apparatus is necessary for a given 
space to be covered. It sometimes 
happens that the manager, without 
consulting the installation specialist, 
orders what would seem to lie the 
necessary equipment, and finds to his 
diSgUSl thai his reproduction is too 
powerful. The reason is thai some 
theatres are so acoustically perfect 

that only 60 per cent of the energy is 
necessary to till them as would he re- 
quired for a theatre of tin- same si/.c 
that was not acoustically Bound. The 

aforementioned manager tin. is that the 

size of his installation far exceeds Hie 

demands of the theal re, and he Is con- 
sequently obliged to operate at greatly 

reduced power. This means that he 
has spent twice as inudi a- was neces- 
sary on the original Installation, ami 
is probably wasting . r ><> per cent of his 
power bin in unneces8arj upkeep. A 
little tailoring here would have saved 
a good deal of Cloth. 

Page 38 

Projection Engineering, September, 1929 

Rotating the "Wax" for Sound Pictures 

Dealing With the Design and Construction of the "Drive" for Disc 


By L. A. Elmer* 

THE machine used in recording- 
sounds on phonograph discs 
synchronously with associated 
pictures consists essentially of 
a turntable, bearing the "wax" and 
rotated by a synchronous motor 1 of 
constant speed, and an electrically 
driven stylus 2 cutting the record. 
In the design of this machine the pri- 
mary aim is to insure that the record 
is both faithful to the original sounds 
and synchronous with the pictures. 
Fidelity in the performance of the 
stylus would be vitiated by departures 
from uniformity in the speed of the 
turntable while sounds were being re- 
corded or reproduced. Although a 
constant speed motor is used, its value 
would be destroyed if the machinery 
transmitting the drive from the motor 
to turntable were not equally free of 
velocity variations. Thus the problem 
of fidelity involves not only the motor 
and the stylus but all the moving 
parts of the machine. 3 

Fig. 2. The mechanical filter for 

the turntable drive, as it appears 

in a commercial disc -recording 


Even were it possible to connect the 
motor directly to the turntable, casual 
variations in the speed would arise, 
from varying frictional loads on the 
turntable and bearings. But direct 
connection is unsatisfacory. Because 
the turntable must operate at a lower 
speed than the motor (one thirty- 
sixth of that speed), reducing gears 
must intervene. In the actual appa- 
ratus the motor drives (through a 
horizontal coupling) a worm engaging 

2 -006 
V) < 

Fig. 1. Above: x < 
The difference ^ 
between actual ~ t 00 * 
and correct po- - JJ 
sitions of teeth >> o 
on a t y p i c a I 5 
gear, relative < a 
to arbitrary ref 
erence position. . 
Below: The"o 
averaging effect J| 5 
of dividing the o 5 
same gear into 5 z 
four layers, cal- 5 o 
culated from *_ 
data (above) % 
for one layer. 


-\A A 

M /A, . ,r 

" ¥ 









a^/vs aAv\ /^w aaA-n vJAa aa/^ -^vIa AAA/> ^V\ 


33 41 4«_ 

120 160 200 240 260 


* Apparatus Development Dept., Bell Tele- 
phone Laboratories. 

a worm wheel which drives (through 
a vertical coupling) the shaft to which 
the turntable is attached. 

It is cyclic speed-change that must 
be guarded against in this mechan- 
ism ; all such changes with frequencies 
from about one-half cycle per second 
up to the higher limit of audibility 
are to be avoided. Speed changes at 
audible frequencies introduce extrane- 
ous sounds into the records, and speed 
changes at frequencies below the aud- 
ible range produce changes in pitch. 
There are in general two points of 
origin for these variations : the turn- 
table and its bearings, and the gears. 
Speed-changing variations in load on 
turntable and bearings are most likely 
to have the frequency of the rotation 
of the turntable (a little more than 
one-half cycle per second). From the 
gears three sorts of variation arise. 
— those accountable to inaccuracies in 
the spacing of the teeth (Fig. 1). to 
errors in the shape of the teeth, and 
to the successive shifts of driving load 
from tooth to tooth. Together these 
may occasion variations with quite a 
range of frequencies. 

Determination of Permissible 

The extent to which these variations 
are permissible is determined, for low- 
frequency changes, by the smallest 
change in pitch the ear will notice 
when pitch-variation is continuous. 
It appears that, when a pure tone is 
projected by a loudspeaker of high 
quality, the ear can detect variations 
in its pitch which exceed one-tenth per 
cent of its frequency. This sets a se- 
vere requirement for constancy of ro- 

It is, furthermore, an overall re- 
quirement, for it applies to differences 
between the original and reproduced 
sound ; and both a recording and a 
reproducing machine intervene be- 

tween these sounds. Since both oper- 
ate at the same speed, and since there 
is a high probability that the ultimate 
record will be lined up on the repro- 
ducer correspondingly to the "wax" on 
the recorder, variations in the speeds 
of the two are likely to be additive in 
their effects upon sound pitch. The 
sum of the variations permitted in the 
two, therefore, must not be greater 
than the total permissible variation 
for the system as a whole. Since the 

Fig. 5. The oil-damping connec- 
tion between the gear and turn- 
table shaft. Above, the oil cup; 
below, the vane-bearing end of 
turntable shaft. 

Projection Engineering, September, 1929 

Page 39 

more its Telocity characteristics are 
made constant the more the apparatus 
costs, it is economical to be stringent 
in requirements for constancy in the 
recorder, of which comparatively few 

are manufactured, and more lenient in 
those requirements in the more nu- 
merous reproducers. An economical 
division between the two machines of 
the total allowable error appears to be 
in the ratio of one to four. The de- 
mand for constancy thus placed upon 
the recorder is far higher than can be 
met by gears and bearings of even the 
most careful construction. It is a de- 
mand which can be filled only by spe- 
cial means. 

Mechanical Filter 

The fact that a continuous, slightly 
varying, motion of this sort is me- 
chanically analogous to a slightly 
varying electric current helps to ex- 
plain what these means are. A pul- 
sating current can be treated as a 
direct current on which small alter- 
nating currents are superposed. The 
suppression of the alternating cur- 
rents, to leave the unvarying direct 
current desired, can be accomplished 
by an electric-wave filter which atten- 
uates the undesired alternating com- 
ponents. The electric filter consists of 
suitably interconnected coils, con- 
densers, and resistances. Since me- 
chanical analogs of these circuit ele- 
ments are respectively to be found in 
masses, springs, and dissipative plas- 
tics, the mechanical-vibration filter 
can be visualized in terms of electrical 

Such a filter, designed in these Lab- 
oratories, is incorporated (Fig. 2) in 
the Western Electric Company's com- 
mercial disc-recording apparatus. It 
uses coil-springs as its capacitances, 
viscous oil for Its resisances, and the 
masses of its moving parts as its in- 
ductances. The great width of the 
frequency band to be attenuated, and 
the pluraliy of the sources of the 
varying-force, considerably complicate 
the problem of determining what 
values of stiffness, weight, and dissi- 
pating ability should be used. For 
example, variations due to gear in- 
accuracies are most readily absorbed 
by very flexible springs, whereas dia 
turbances dtle to varying loads are 
best prevented from affecting turn- 

1 //. \r. 8 toller, Record, November, 1828 

-IF. A. Frith rirl;. Record, Vniimhrr. [928 

"■ To be described in the Journal of thi 
American Society of Mechanical Engineers 

Hi in tin I nmn. 

springs. This structure also multi- 
plies by four the frequencies with 
which these disturbances occur, since 
each inaccuracy in cutting is made to 
occur once for every 90 degrees, in- 

Fig. 3, above: The reduction gear- 
ing: a worm and a four-layer 

Fig. 4, left: The spring connection 
between the gear and turntable 


Fig. 6, right: Linkage mechanism 

and its braces, through which the 

gear drives the oil cup. 

table speed by the use of stiff springs. 
The filter finally designed embodies a 
compromise between these conflicting 
demands. Its general construction is 
such that the worm-driven gear drives 
the turntable shaft through the lin- 
early flexible springs, and relative mo- 
tion of the gear and shaft is damped 
by the oil. 

The gear (Fig. 3) is made in four 
layers. These layers are clamped to- 
gether when the teeth are cut, and 
each layer is afterwards rotated 
ninety degrees relative to the adjacent 
layer. All are finally mounted, in en- 
gagement with the worm wheel, so 
that each can move independently of 
its companions. To each layer two 
cross-braced posts are rigidly at- 
tached, from the tops of which (Fig. 
4) springs lead to lugs on a plate 
fastened to the turntable shaft. Thus 
each layer of the gear independently 
drives the shaft through two springs. 
It is apparent that the offset four- 
layer structure of the gear divides by 
four the amplitudes of the disturb- 
ances caused by inaccuracies in the 
teeth, since at any one time, each af- 
fects but one of the four sets of 

stead of once for every 360 degrees, 
of rotation. This higher frequency 
is far more readily absorbed by the 
filter than the lower would be. 

The oil connection between gear and 
turntable shaft is effected by permit- 
ting the layer-gear to rotate a vane- 
bearing oil-filled cup, into which dip 
vanes attached to the turntable shaft 
(Fig. 5). The mechanism (Fig. 6) 
through which the gear drives the cup 
is in this case rigid rather than elas- 
tic, but is again one whereby the effect 
of a gear irregularity upon the cup is 
quartered in amplitude and quad- 
rupled in frequency. This mechanism 
is a system of links independently 
driven by each of the layers of the 
gear so as jointly to rotate the cup 
with their average velocity. To each 
layer, again through the perpendicular 
posts, is attached a link (Fig. 7). The 
members of one and the other pair of 
these links are flexibly joined by cross- 
links, to the center of each of which 
is pivoted one end of a bell crank. 
The other ends of these two bell-cranks 
are in turn flexibly joined by a third 
cross-link, to whose center the mem- 
ber which drives the cup is attached. 

Fig. 8. Steps in the development of the linkage, showing its successively 
more rugged construction. 

Page 2,0 

Projection Engineering, September, 1921) 

It is apparent that the motion of the 
center of each cross-link is the aver- 
age of the motions of its two ends. 
Each of the first two cross-links, 
therefore, averages the motions of two 
of the gear-layers, and the third cross- 
link averages the motions of the first 
two cross-links, driving the oil cup 
with the average motion of all four 

Elimination of Backlash 

Because the deflections with which 
this apparatus is expected to operate 
are very small, it is essential that no 
motion be lost by "backlash" in pivots. 
For this reason, and to minimize 
pivotal friction, flat reed-springs are 
used for all joints. Since the linkage 
cannot be constructed in a single hori- 
zontal plane but must be built in sev- 
eral planes, it is subject to warping 
forces which tend to produce velocity 

errors. To avoid these, the linkage is 
extensively braced (Fig. 8). 

In the development of this filter, re- 
liance upon theory had to be supple- 
mented by measurements of the ef- 
fectiveness of various models. Since 
smooth rotation of the turntable was 
in view, fluctuation in turntable speed 
was the performance to be directly 
measured. This was accomplished 
stroboscopically. On the rim of the 
turntable 216 accurately spaced grooves 
were cut. A disc, with six radial slots, 
was connected by a rigid drive to the 
shaft of the synchronous motor. The 
disc was so placed that the grooves on 
the rotating turntable could be ob- 
served one by one by a microscope 
looking through the slots in the ro- 
tating disc. Observed through this 
apparatus, the groove on the edge of 
the rim appears to stand still when 
the speed of the turntable is exactly 

"* + 

= Av. Turntable Vel. 

Max. Turntable Vel. 

= Min. Turntable Vel. 

: Angular Velocity of Vibration = 2 s f. 

2 = Velocity Variation 


200 = Velocity Var. in per cent. 

U) T CO 

200 = 200 

U) , R w x 

II = Amplitude in Radians 

When = I, zoo = 200 

w, to. R 

Fig. 9. Method of converting stroboscope micrometer reading to per cent 
velocity variation. The curve of large radius represents the rim of the 
turntable, and the curve of small radius represents the familiar diagram 
of harmonic motion. At the prolection of the end of the small circle's 
radius is a groove on the turntable rim. The quantity read on the microm- 
eter is 2i — the maximum motion of a groove. 

Fig. 7. Schematic diagram of link- 
age.' The bell-cranks are pivoted 
at the- mechanism's center, but are 
not attached to the shaft. The 
third cross-link, between the ends 
of the bell-cranks, is perpendicular 
to the plane of the diagram. From 
its center extends the only mem- 
ber which has a rigid connection 
at the center of the mechanism, to 
the collar which drives the oil cup 

one thirty-sixth the speed of the 
motor. A small error in turntable 
speed causes the image of the groove 
to change position momentarily. The 
amount of this shift can be read in 
thousandths of an inch on a filar mi- 
crometer placed in the eyepiece of the 
microscope. From this reading the 
per cent velocity variation can be cal- 
culated (Fig. 9). 

The model finally developed drives 
the turntable with remarkable con- 
stancy. Of the velocity variations 
from the two major sources of error 
■ — from varying loads, at one cycle 
per revolution, and from varying 
gear-spacing, at four cycles per revo- 
lution — the former has been reduced 
to 0.04 per cent and the latter to a 
point below the limit of measurement. 
Supplemented by suitably modeled 
drives for reproducing machines, re- 
cording drives of this type provide 
ample insurance against maltreatment 
of sounds by driving machinery. 

Projecting Films on Metal Prisms 

New Metallic Screen Developed Abroad Materially Reduces Arc 

Current Required 

LAMINATIONS of gold and other 
metals, together with pigments 
of various reflective properties 
are being offered as a means of 
achieving a super-reflective screen. 

Engineers, working for eight years 
in this country and abroad, have 
evolved a screen which, it is said, has 
reflective properties so high that 
amperage, which sometimes has been 
increased with sound, may now be re- 
duced to less than one-half and still 
give projection as good as or better 
than before. This, at least, is the case 
with the Film Guild Cinema, which is 
the first New York theatre to install 
the new screen. 

"From 25 amperes, the current has 
been reduced to 12y 2 amperes," 
Symond Gould, director of the theatre, 
declared. "That is as low as the pres- 

ent rheostat will go, but I believe that 
from five to ten amperes will be suf- 
ficient for any house up to a thousand 
seat capacity using this type of 

A three-inch strip of this surface, 
seen through a magnifying glass, 
looks like a blaze of diamonds. The 
pigments and the metals on its granu- 
lated face build up myriads of prisms. 
These reflect light from one to the 
other. When one considers that there 
are many of them to the square inch, 
one may get some idea of the highly 
reflective properties of the whole. The 
prisms give an equal reflection on each 

The screen is made in both perfor- 
ated and unperforated form. The sav- 
ing in current, for the smallest theatre, 
is said to be at least ten dollars a day, 

increasing proportionately with the 
larger houses. 

The screen is non-oxidizing and 
weatherproof. It may be washed and 
scrubbed. It won't peel and it won't 
turn black. As proof of this, it is cited 
that a piece of it left out of doors for 
years at a time, was subjected to tests 
which indicated that it was just as 
good, if not better, than before — better 
perhaps, because it has a tendency to 
whiten with age. The absence of 
aluminum in its make-up is respon- 
sible for its non-oxidizing properties. 

The screen is made in a graded 
series, so that each theatre may be 
fitted with a surface having the exact 
reflective angle to give every patron 
an evenly illuminated picture. This 
will be done with the least light waste 

Projection Engineering, September, 1929 

Page ! t l 

New Musical Effects Produced by 
Electrical Means 

New Freedom of Musical Expression Gained Through the Use of High 
Power Sound Reproducing Devices 

By Edward W. Kellogg* 

ONE of the most striking recent 
developments in the art of 
sound reproduction is that of 
loudspeakers capable of deliv- 
ering large volume of sound. The gain 
from this increase in loudness is not 
simply that the ears are relieved of 
strained attention to catch what is said 
or played, but a change of quality as 
judged by ear occurs as the loudness is 
altered, even when the actual sound 
wave shapes are kept the same. 1 For 
this reason, reproduced speech and 
music will not sound natural unless 
the reproduction is at approximately 
the same loudness as the original. 

The advent of the Radiola No. 104 
brought radio music into the home 
with a volume about equal to that of a 
piano in the room. Electrical repro- 
duction was then applied to phono- 
graphs, and the Brunswick "Pana- 
trope" and Victor "Electrola" far ex- 
ceeded the machines depending on 
direct or mechanical reproduction, in 
point of sound power. 

Auditorium Speakers 

More recently there have been 
evolved loudspeakers of much higher 

1 "Auditorn Maskino of One Pure Ton'' 
by Another," R. L. Wepel & C. E. Lane. 
Phys. Rev., Vol. 2.3, P. 266, 1924. 

"Physical Measurements of Audition " 
B. F. Fletcher, Bell System Tech. Jour , 
Oct. 1923, P. 145. Jour. Franklin Inst.. 
Sept. 1923. 

"High Quality Transmission and Repro- 
duction of Speech and Music," W. II. 
Martin and H. Fletcher, A. I. E. E., Vol. 
XLlll, 1924, P. 385. 

MR. KELLOGG convinces 
us that the art of mu- 
sical expression is to be 
enriched by means of 
electrical reproduction. 

That a purely commercialized 
device will hitch itself to the 
purely aesthetic and remain as a 
contribution to the art of all 
sound expression appears far 
fetched. The fact remains, hoic- 
ever, that with tlir aid <>)' super- 
power reproducing devices, qnnl- 
itii and volume can be controlled 
independently and an entirely 
new form of musical expression 

That point of development has 
been reached where we can 
"make the heavens resound to a 
whisper." We shall yet experi- 
ence the thrill of our bodies 
vibrating under the power of 
"a soft musical passage'' rising 
alinre the orchestral background 


'Research Laboratory, General Electric 

power lor use in auditoriums or out- 
of-doors. In these devices no pains are 
spared to secure faithfulness or high 
quality, and amplifiers of ample ca- 
pacity are employed to avoid distor- 
tion. Speakers of this class have for 
the most part been of two types, one 
employing a large horn, perhaps 12 to 
20 feet long, with a bell opening of (he 
order of 8 feet by 8 feet, while the 
other type employs a number of cone 
type speaker units. As an example of 
the cone type auditorium speaker a 
model buill about two years ago under 

Mr. Edward W. Kellogg, and the high-power amplifier and bank of dynamic 
speakers employed in the interesting experiments discussed in this article. 

the writer's direction may be briefly 
described. It employed nine coil-driven 
cones such as used in the Radiola No. 
104, the units being arranged in three 
racks, of three cones each. The power 
stage of the amplifier consisted of a 
pair of UX-851 tubes, each drawing .3 
ampere plate current at 2000 volts. 
The amplifier could supply about 150 
times the power without distortion 
which the UX-210 tube can supply to 
its cone in the Radiola No. 104 or the 
Panatrope. This equipment was used 
in a number of public gatherings at 
which orchestras or bands were pres- 
ent. It could, with pleasing effect, be 
run at a setting at which it was defi- 
nitely louder than a ten to fifteen-piece 
dance orchestra, or comparable with a 
military band. 

Violin at Band Volume 

In the course of these demonstra- 
tions one characteristic of the music, 
produced by means of the high power 
speaker, impressed itself on those of 
us who were present. It is as easy to 
get a powerful sound from a single 
voice or instrument as from a large 
number of voices or from a whole 
orchestra. In fact we can with a 
given equipment put out considerably 
more sound power when reproducing a 
single voice or instrument than when 
reproducing the highly complex sounds 
of a large chorus or orchestra. Phono- 
graph records are usually so cut that 
a vocal or instrumental solo is practi- 
cally as loud as a hand recording. 
What this means with the household 
phonograph is that the BOlO numbers 
are reproduced with somewhere near 
their original volume, hut that the 
orchestra and hand numbers, while 
loud enOUgh to he enjoyed. ;ire faint 

Imitations of n iglnals. The high 

power auditorium speaker can practi- 
cally duplicate the orchestra, chorus. 

or band, but it can do something which 
has not been possible before sing n 
tenor or soprano solo, or play a violin 
Si band volume. 

Sew Musical Expression 

such reproduction It of course nol 
exactly "natural," bul the function of 

:i mUSlCBl device, such as the loud 

speaker, is not necesarily limited to 
Imitation I although II musl be capable 
of Imitation) bul to afford pleasure 
to the listener. And one of the ele- 
ments which brings a thrill to the 

listener is the flood of sound that 
shakes his whole body, that in some 

passages Beema even deafening, The 

Page 42 

Projection Engineering, September, 1929 

ability to reach such sound levels ex- 
tends the range of musical expression, 
and carries an impression of power. 
Why else do we build giant organs, 
organize choruses of hundreds of 
voices, bands of fifty pieces, and orches- 
tras of a hundred or more instruments? 
It will be argued that the large 
orchestra is necessary to afford the 
desired variety of instruments and to 
give proper balance. But if there are 
several instruments of each kind, this 
explanation can hardly stand. Still 
less do such reasons apply to the two 
hundred voice chorus. A quartet, or 
for some compositions a sextet, can 
carry all the parts, afford the full 
range of voice qualities, and can be 
controlled and blended more perfectly 
than a larger number of voices. There 
is, of course, a psychological factor in 
favor of the large orchestra or chorus, 
but the primary purpose is to produce 
a great volume of sound. 

Altered Sound Quality 

The multiplication of sound sources 
results inevitably in a change of 
sound quality, the wave shape from 
the multiple source being more com- 
plex. With the best of tuning, two 
different instruments playing the same 
note will produce more or less rapid 
beats. With a large number of instru- 
ments playing the same note, each will 
beat with all the others, and the result 
is rapid and rather irregular fluctua- 
tions in intensity during the playing of 
each note. Whether the net effect is 
pleasing to the ear is perhaps a matter 
of taste. Those who prefer the com- 
plex tones would probably describe 
them as "richer." Those who like the 
simpler tones would speak of them 
as "mellow" or "smooth" and find, rela- 
tively, a certain harshness in the com- 
plex tones. 

Heretofore we have had no choice 
but to accept the complex wave and 
the tonal qualities which it carries, 
whenever we have wanted great sound 
volume. The two factors have gone 
hand in hand. With the new tool at 
our disposal, the high power sound 
reproducing device, we can control vol- 
ume and tone quality independently, 
and can have the smooth and mellow 
tones of the small group or single 
instrument at any volume. There is 
thus a new freedom given to musical 
expression. The quality resulting from 
blowing or bowing strongly can be 
reproduced softly as desired, or the 
quality of an instrument played softly 
may fill the auditorium. Still more 
important is the advantage to be 
gained in the rendering of vocal selec- 
tions. Every voice changes in quality 
according as the person sings loudly or 
softly, and the change is certainly in 
the direction of an impairment in qual- 
ity as the loudness approaches the 
point where strain and effort are pres- 
ent. The forced voice gives no pleas- 
ure and is likely to result in perma- 
nent injury. We seek the world over 
for the rare combination of great 
power, pleasing voice quality, and 
sufficient musical appreciation and 

training to use the voice with artistic 
effect. But there are thousands of 
singers who have all of the require- 
ments except power, and whose voices 
may even surpass those of their more 
celebrated brothers or sisters in rich- 
ness and fineness. These voices are now 
made available in the theatre and audi- 
torium as well as in the parlor. All 
singers may use their voices at more 
natural levels, and the smooth round 
tones of the soft or subdued voice may 
be heard with ease in all parts of the 

Amplifying a Whisper 

Certain difficulties are encountered 
in the attempt to magnify the voices 
of singers actually present on the 
stage, and the full advantage of elec- 
trical sound production cannot perhaps 
be realized under these conditions. 
But where music is recorded and then 
reproduced the new factors will be- 
come of great importance. Already the 
alteration of sound levels possible with 
electrical phonograph recording and 
reproduction has been utilized to pro- 
duce records of a type that has been 
quite popular, namely, the "whisper- 
ing" tenor solo. The microphone is 
placed very close to the singer, who 
speaks and sings in a voice little above 
a whisper. On the higher notes the 
voice becomes nearly a falsetto. The 
reproduction is many times louder 
than the original, and the effect is of 
a voice of very unusual quality. Those 
who listen probably do not often real- 
ize the discrepancy in loudness, and 
might not like it so well if they did. 
We have so long been seeking natural- 
ness in reproduction that unnatural- 
ness is thought of as a fault, even 
though it may have been brought 
about for a purpose and with pleasing 

Although a large orchestra is looked 
upon as the finest that can be provided 
in musical entertainment, it may be 
predicted that where recorded music 
is used, the aim in general will not 
be to give the best possible imitation 
of the large orchestra (although this 
can be done with remarkable success 
when desired), but to render in what- 
ever volume is wanted the simpler 
music of a small orchestra, with single 
instruments instead of groups of in- 
struments carrying melodies. Balance 
is not dependent on the use of the 
proper number of instruments of each 
kind, but can be controlled by the posi- 
tions of the players relative to the 

The Orchestra of the Future 

Let us venture another prediction, 
farther probably from early fulfill- 
ment. The orchestra of the future will 
make extensive use of electrical sound 
producing devices. One of the most 
important applications will be to ac- 
centuate the tones of certain instru- 
ments in order that a single instru- 
ment may carry a melody, or to give 
the effects of accompanied solos with- 
out subduing the entire remainder of 
the orchestra. Again new tone qualities 

are obtainable by electrical means. 
For example, let us suppose that an 
electrical sound pickup is located 
within the instrument whose tones are 
to be magnified. The character of the 
tones will vary with location and also 
with the design of the electrical pick- 
up or microphone. Instruments which 
are not at present loud enough to be 
useful, except in the softer passages of 
the composition, will be made useful 
for the loud passages as well. With 
such electrical assistance as has been 
suggested, the orchestra of the future 
will be able to produce many effects 
not now possible. 




THE first sound picture or talk- 
ing movie designed especially 
for purposes of military instruc- 
tion was completed recently and 
shown before a representative group of 
military and naval officials. The film 
was made at the Infantry School at 
Fort Benning, Georgia. It is a result 
largely of the Western Electric Com- 
pany's experimental work and produc- 
tion methods. 

One of the "most difficult of all 
production tasks," to quote the com- 
pany's statement, was placed before 
the Hawthorne organization of the 
Western Electric Company by the en- 
thusiastic public reception of the talk- 
ing pictures. 

More than $500,000 worth of the 
most modern machine equipment had 
to be bought and especially adapted to 
this project. A heavy production 
schedule was set up. The tool room 
was geared up to capacity for turning 
out the required tools. A storeroom 
covering 6,500 square feet of floor 
space was built in record time for the 
storage of material, process parts and 

Accuracy and precision were the 
basic features in the planning. One 
ten-thousandth part of an inch was a 
familiar item. The finest work was 
necessary in the manufacturing proc- 
esses entailed in making the new con- 
denser type transmitter (the micro- 
phone used in recording for the talk- 
ing pictures). One small disc, a part 
of the transmitter, must be ground 
until its; surface is exactly flat — mi- 
croscopically flat. To test this flatness 
a quartz disc is used. By placing this 
disc on top of the other disc, a patch- 
work of light rays broken into spec- 
trum rays is seen. If this patchwork 
of light rays does not have a certain 
design then there is something out 
about the flatness of the manufactured 

Dust-proof rooms are used for trans- 
mitter assembly. Dust, any speck of 
it, in this instrument, would be fatal. 
Glass cabinets, with all the moisture 
exhausted, contain the parts which are 
assembled in the cabinet. The work- 
men place their wrists through rubber 
sleeves fixed to the cabinet in order 
to assemble the parts. 

Executives Service Bulletin. 

Projection Engineering, September, 1929 

Page /,S 

The Acoustimeter 

An Electrical Means for Measuring Sound Intensities 
By R. F. Norris* 

IN development work of any kind, 
it is necessary to be able to meas- 
ure very slight degrees of progres- 
sion or retrogression, which in 
themselves are of no great importance 
but which may indicate clearly the 
course to be followed. These almost 
imperceptible indications are the 
straws which tell us which way the 
wind blows and but for them we 
might waste a great amount of ex- 
pensive effort in directing our investi- 
gations in wrong and barren paths. 
Briefly, the first tools of the investi- 
gator are accurate and dependable in- 
struments with which his progress may 
be measured, be it ever so slight. If 
such instruments are not available, he 
had better lay aside the seemingly 
more important parts of his work un- 
til they have been developed. Other- 
wise he may miss the guide posts 
which are to lead him to his goal. 

This is particularly true of acousti- 
cal work since the ear, which is the 
obvious instrument of comparison, 
while sensitive to very minute sounds, 
responds to their stimulus in a pe- 
culiar way. The physical loudness or 
intensity of a given sound is measured 
by the square of the amplitude of its 
wave while its apparent loudness to 
the ear is ten times the logarithm of 
this intensity. That is, a sound having 
a physical intensity of 1,000.000 
will have a loudness factor of 10 log. 
1,000,000 or 60, while a sound of only 
one-tenth the physical intensity 100,000 
will have a loudness factor of 10 log. 
100,000 or 50. Tims though the physi- 
cal loudness <>f the second sound is 
only one-tenth thai of the first, it 
will sound five-sixths ;is loud. From 
this simple Illustration it is evident 
that the car is of little or no use in 
tho measurement of physical intensi- 
ties of sound. Yet in the problems 
to be investigated such measurements 
were of prime importance. An Instru- 
ment which would ii<> ragged, reliable, 
and not affected greatly by small 

variations in pitch was soughl with- 
out success. It was. therefore, neces- 
sary to develop such an Instrument, 
instruments of several designs were 
built and discarded, the good points of 
each being retained until In this proc- 
ess of evolution the instrument now 

in use w;is evolved. The present in- 
strument though far from perfect, 
gives reliable results, is ragged enough 
to be transported with Impunity, and 
retains its calibration to an amazing 

The instrument consists of an elec- 
trical sound pickup, a four-stage, 

* ciiirf Engineer, 0. P. Bwrgeei, Labora- 
tories, tnc. 


Schematic diagram of the Acoustimeter. The pickup is not shown connected 

in the circuit. 

transformer-coupled audio amplifier, a 
resistance network which, while keep- 
ing the output inpedence constant, 
provides a gain control by which the 
range of the instrument may be con- 
trolled : a vacuum thermocouple and a 
very sensitive millivoltmeter. 

Magnetophone Pickup 

The sound pickup is a magneto- 
phone of the Baldwin type. The 
sound waves to be measured impart 
a motion to the diaphragm which is 
proportional to their amplitude. This 
motion generates a minute current 
which is also proportional to the am- 
plitude of the sound waves. This 
small current is amplified by the am- 
plifier and fed in whole or part to the 
thermocouple, which supplies a direct 
current to the millivoltmeter, which 
is proportional to the square of the 
current from the amplifier. since 

the intensity of a sound is the square 

of the amplitude of the sound waves, 
nnil since the current is proportional 
to the square of the current which is 
generated by the pickup, the meter 

reading may be Said to be true in- 
tensity units. To evaluate these units. 

the Instrument must be calibrated. 

To do this a sound source of such :iii 

Intensity as to give a readable Indica- 
tion on the meter Is placed one foot 

from the pickup. Tl bservers then 

move away from the source to such a 
distance thai the sound just becomes 
inaudible. The average distance for 
nil the observers Is measured and the 
Loudness of the sound :ii the pickup 
may be computed .-is follows: Say the 
average distance Is K) feet. The audi 
billty of the sound at K) feet Is then 
and the Intensity Is log or I, The 

formula representing sound intensity 
at various distances from the source is 

d 3 ' 

Where T is intensity. K = a 

constant depending on the loudness of 

the source and d is distance from the 

source. Substituting 40 feet for d. we 


have I = ■ or K = 1000. Our con- 


stant is now determined for this case 
and the intensity at the pickup, which 
is 1 foot from the source, will obviously 

he I = — or 1600 physical units. 

Dividing this value by the number 
of divisions registered by the instru- 
ment meter, we obtain the value of 
each division i i i intensity units. Since 
this calibration method is tedious and 
inconvenient, it is fortunate that in a 
majority of the work encountered rela- 
tive results only were required in 

w hi,h the calibrat ion factor of the In- 
strument cancelled out of the final re- 
suits, making frequent recalibrations 
of minor Importance. 

/ pplU -nt ions 
Willi this Instrument which h:is been 

named the Acoustimeter, a consider- 
able amount of work ims been done 
in the design of sound proof partitions, 
gas engine mufflers, sound absorbing 
window ventilators and the Investiga- 
tion of fault] auditorium acoustics. In 
each of these Investigations, very 
^n^iii differences of sound Intensity 
wen- found to be the deciding factors 
in the direct ion of the re earch and in 

the final solutl f the problems 


Projection Engineering, September, 1929 

Light-Sensitive Cells 

Practical Cells of Various Types 
By John P. Arnold 

I. Photo-Conductive Cells 

ANY brief discussion of cells of 
the photo-conductive ■ class 
b from the practical standpoint 
must be confined mainly to 
those employing annealed selenium for 
the light-sensitive material. It is true 
that some research has been made in 
recent years with compounds of anti- 
mony, bismuth, copper, lead, molyb- 
denum, silver, thallium, etc., but the 
results of such investigations have not 
led to the development of light-sensi- 
tive devices which are greatly superior 
to the selenium cell, excepting possibly 
the thallium cell to be described below. 
The literature in reference to seleni- 
um is voluminous, and the reader who 

1. A sketch of a typical 
selenium cell-form. 

wishes to study the subject thoroughly 
should consult the bibliography com- 
piled by M. F. Doty, "Selenium: A 
List of References, 1817-1925," pub- 
lished by the New York Public Library, 
1927. Of particular interest are the 
references to its physical and chemical 
constants, its electrical and optical 
properties, the cells and their uses, 
and also the early patents relating to 
visual communication, sound record- 
ing, etc. 

Light action in selenium was first 
reported fully in 1873 by Willoughby 
Smith who used bars of this element 
for high resistances. When sunlight 
fell upon them, it was observed that 
their conductivity increased. While 
useless for the purpose for which they 
were intended, the curious phenomenon 
exhibited soon led to the development 
of the first practical instrument for 
controlling an electrical current by 
means of light. 

Essentially a selenium cell com- 
prises two metallic electrodes between 
which annealed selenium is deposited. 
As the specific electrical resistance of 

selenium is quite high — 30 to 2500 
megohms per cubic cm. (Bidwell) — 
the cells should be so designed that 
only a short path of relatively large 
cross-section is traversed by the cur- 
rent flowing between the electrodes 
when these are connected to a source 
of potential. Furthermore, the se- 
lenium should be spread in a thin film 
so that a relatively large area, with 
respect to its volume, is affected by the 
light. The films should not be thicker 
than 0.0014 cm., as Brown 1 has shown 
that this is the effective depth for the 
penetration of light into the surface of 
the element. To obtain the greatest 
ratio between the light-dark current 
(sensitivity) and to lessen inertia 
(the lagging of the electrical response 
behind instantaneous changes of illumi- 
nation), this latter requirement should 
always be fulfilled in preparing the 
cells. At one time it was thought that 
the heat treatment or annealing 
process was a very important factor, 
but Piersol, in a paper referred to 
later, states that neither the length of 
time nor the temperature (within 
certain limits) is at all critical. 

Before discussing a few practical 
cells, it is necessary to point out the 
materials which are used for their 
construction. We have three compo- 
nents : the conducting electrodes, the 
insulating base, and the selenium film. 
As a number of metals will oxidize at 
the annealing temperature and com- 
bine with the selenium as a selenide, 
platinum, gold and nickel are the best 
materials to use, but due to the 
expense of gold and platinum, such 
metals or alloys as copper, aluminum, 
zinc, brass, Constantin, German silver, 
and also graphite and carbon may be 
employed. Unfortunately, however, 
selenium films seem to adhere better 
to those metals which oxidize than to 
those which do not. For insulation, 
quartz, glass, porcelain, slate, mica, 
soapstone, and bakelite are most satis- 
factory in preventing leakage currents 
across the electrodes of the cells. Of 
the various allotropic forms of se- 
lenium, the grey crystalline metallic 
variety alone has the suitable light- 
sensitive property, and the object of 
the annealing process is to convert the 
commercial forms of selenium to this 

Various cell-forms have been sug- 
gested, but perhaps the most satis- 
factory is the grid arrangement shown 
in Fig. 1. Here a thin film of metal 
is deposited either by electrolysis, 
cathode sputtering, photograving proc- 
esses, or some similar method. Mc- 

Mahon and Brown 2 prefer gold and 
platinum paints consisting of colloidal 
solutions of the metals in essential oils. 
The base (b) may be quartz or sand- 
blasted glass, and the metallic film is 
divided into two electrically con- 
ducting portions, as shown. The se- 
lenium film bridges the gaps between 
the two electrodes or, by the method 
of the investigators mentioned above, 
large crystals of selenium are em- 
ployed. Wires leading to the binding 
p'osts of the cell are attached to the 
electrodes (a, a) by means of Wood's 

After a film is deposited on the 
form, it is then necessary to convert 
the selenium, usually from an amorph- 
ous variety, to its light-sensitive form. 
Piersol 3 describes a process of anneal- 
ing by means of which "several hun- 
dred selenium cells have been made 
with identical characteristics." He 
anneals the cells at 180 deg. C. for five 
minutes. An electric oven is often 
used for this purpose when accurate 
temperature control is desired, al- 
though a Bunsen burner is satis- 
factory in most cases. 

An even simpler construction than 
the foregoing has been proposed by 
Martin* made by heating powdered 
vitreous selenium to 216 deg. C. in a 
test tube and allowing it to cool slowly. 
By turning the test tube nearly upside 
down, long threads of selenium can be 
poured out, their diameters depending 
on the temperature. Threads about 
2 cm. long and 0.1 cm. in diameter 
were found to be most satisfactory. 
These threads were annealed and then 
strapped down on a microscope slide 
by wires at either end. Cells so con- 
structed are said to have a resistance 
of about V 2 megohm. 

It is advantageous to place a se- 
lenium cell in a vacuum to prevent the 
absorption of moisture. Ruhmer 5 sug- 
gested this improvement in design. He 
cut double parallel threads in soap- 
stone or unglazed porcelain tubing and 
into these grooves wound No. 40 B&S 
gauge wires, which were secured at one 
end to the base of an incandescent 
lamp. The soapstone or porcelain tub- 
ing was divided in two pieces in order 
that wedges could be inserted to take 
up the expansion of the wires during 
the annealing of the cell. The bulb 
was then evacuated. Such cylindrical 
cells may be placed at the focus of a 
parabolic reflector and illuminated 
from all sides. 

1 Pliys. Rev., Vol. 34, p. 201: 1912. 

2 Jour. Opt. Soc. Am., Vol. 11, p. 223' 

3 Phys. Rev., Vol. 30, p. 664 ; 1927. 
* Jour. Opt. Soc. Am., Apr., 1928. 
f'Das Selen," p. 11; Berlin, 1902. 

Projection Engineering, September, 1921) 

fuge 45 

As to resistance of cells, they may 
be divided into two classes (1) high 
and (2) low resistance cells. The 
former type have a dark resistance 
(when they are not illuminated), vary- 
ing usually from 100,000 to 500,000 
ohms, while the low resistance cells 
from 100,000 to about 10,000 ohms. 
There is very little difference between 
the two, although high resistance cells 
often have greater sensitivity. For 
engineering work, due to various cir- 
cuit constants as well as ordinary 
electrical apparatus, cells of fairly low 
resistance are often to be preferred. 

The theory of light action in seleni- 
um is explained by Fournier d'Albe. G 
as due to the ionization of the selenium 
atoms. The current due to the acting 
light varies as the square root of the 
illumination. Selenium is more respon- 
sive to light of longer wavelength than 
any of the photoelectric cells of the 
alkali metal type, this sensitivity also 
extending into the infra-red spectrum. 
It will be noted that the increased 
conductivity of selenium under the 
action of light is fairly rapid, but the 
return to the dark resistance value is 
much slower, varying from several 
minutes to a number of hours, accord- 
ing to the intensity and duration of 
the excitation. This fatigue character- 
istic is more or less noticeable, depend- 
ing largely on the fulfillment of the 
conditions of design and construction 
mentioned in the beginning of this sec- 
tion. However, both the fatigue and 
lag of cells prevents their satisfactory 
use for many applications although 
they can be employed in many cases, 
especially in places where they are 
used in connection with a relay for 
short intervals of illumination with 
relatively longer rest periods between 
successive illuminations. 

The following facts regarding the 
care of cells should always be 
observed : 

1. Keep cells cool. The heating 
effect of passing too large currents 
through the cell, or from the exposure 
to intense radiation, will cause the 
formation of selenides of the metal 
electrodes. Gold selenide is indicated 
by the appearance of dark brown spots 
on the surface of the selenium. 

2. Apply the lowest voltages that 
will give the desired results. The use 
of high-resistance relays is preferable, 
or a limiting resistance may be placed 
in series with the cell for protective 
purposes. In general, ten milliamperes 
or more should not pass through the 
cell, but it is always best to follow the 
manufacturer's instructions in this 

3. Cells should not be exposed to 
intense light for long intervals of time. 
The cell becomes fatigued and becomes 
temporarily (or even permanently) 
insensitive to light. 

4. Keep cells dry. If not sealed in 
to exclude moisture, they should be 
kept in a box containing a few pieces 
of calcium chloride. 

Fig. 2. The Case Thalofide cell, 
which is particularly sensitive for 
the infra-red end of the spectrum. 

5. When not in use, cells should be 
kept in the dark, but they may be 
exposed to light regularly, for short 
periods, to aid in retaining their 

6. If the resistance of a cell drops 
greatly, it can be raised, at least 
temporarily, by applying pulsating or 
alternating currents. 

Case 7 discovered that thallium sul- 
phide is not only sensitive to light, but 
also has a maximum in the infra-red 
region of the spectrum and, therefore, 
such a cell can be controlled by radia- 
tions invisible to the human eye. In 
his earlier work, Case made use of 
thallium sulphide, but later refers to 
thallium oxysulphide, having found 
that the slightly oxidized compound is 
more active under illumination. 

Case fuses the material at about 
650 deg. C, the fusing point of the 
compound, in the presence of air, thus 
forming thallium oxysulphide. The 
thickness of the material is usually 
between 0.3 and 0.5 mm. After fusing, 
it is immediately and rapidly cooled. 

The Case cell (Fig. 2) of this type 
is called the "Thalofide" cell. The con- 
struction consists of a quartz disc, %- 
inch in diameter, which is coated with 
a film of lead and this latter is cut in 
a grid form similar to that shown in 
Fig. 1. Leads are soldered on after 
the thallium compound has been 
applied. The assembly is sealed into 
an evacuated glass bulb. 

The actual light-sensitive surface ex- 
posed is about 2 mm. wide and from 
10 to 12 mm. long. 

The average sensitiveness of these 
cells is such that the dark resistance 
is lowered by 50 per cent., in 0.02 foot- 
candle when the source of light is a 
tungsten filament. In some of the best 
cells this drop is obtained in 0.004 foot- 
candle. The dark resistance of dif- 
ferent cells may be anywhere from 5 
to 50 megohms, depending primarily 
on the nature of the material used and 
to the grid spacing. This high resist- 
ance could be reduced by making the 
grid of 100 or more lines per linear 

Thallium oxysulphide appears to 
undergo a slow photo-chemical change 
without the use of a color filter. This 
is supplied with the commercial cell. 

The thalofide cell responds quickly to 
the exciting radiation, usually com- 
pleted after a lapse of 15 seconds. On 
longer exposures, the galvanometer 
deflection increases slowly and some- 
times irregularly. Although the time 
—two minutes to obtain maximum 
response — is shorter than molybdenite, 
the thalofide cell behaves somewhat 
like it, requiring twice as long — about 
four minutes — for complete recovery. 
For small deflections, as an exposure 
of one minute, two minutes for 
recovery is sufficient. 

//. Photoelectric Cells 

Allen 8 has traced their historical 
development from the early Elster and 
Geitel alkali hydride cell down to all 
but the more recent types developed in 
this country. Some of these are of 
particular interest and will be de- 
scribed here. 

Hughes 9 designed a cell which sug- 
gests the black-body inclosures used in 
the study of heat radiation. A pear- 
shaped flask traps practically all of 
the light that enters the cell through 
the window and by progressive reflec- 
tions from the interior walls produces 
electronic emission wherever it im- 
pinges on the light-sensitive cathode. 

Small cells — two, three or four 
inches in diameter — are usually suit- 
able for all applications except tele- 
vision. For such communication both 
large or small cells are used depend- 
ing on the method of scanning. The 
two methods are often termed direct 
and reflection scanning. In the former 
case, the subject to be transmitted is 
strongly illuminated and placed before 
the scanning apparatus; for instance, 
the conventional Nipkow disc. An 
image of the subject is thrown on the 
disc by means of a lens. The photo- 
electric cell collects the light that falls 
upon it through the apertures in the 
disc. This optical system is less 
efficient than that employed in the 
reflection method where a small beam 
of light is made to pass over the sub- 
ject by the rotation of the scanning 
disc and large photoelectric cells col- 
lect the diffused light reflected from 

'The Moon-Element," Chop. TIT. 

\Phys. Rev., Vol. 15, p. 289; 1920; Jour. 
Opt. 80c. Am.., Vol. 6, p. 398 ; 1922. 

s "Photo-electriciti/," Chap. XVII; 1925. 
9 Philo. Man., Vol. 35, P. 679: 1913 also 
his "Report on Photo-electricity," p. 104. 

Page Jf6 

Projection Engineering, September, 1929 

the subject. The advantages and dis- 
advantages of these systems are fully 
discussed by Gray and Ives. 10 

Various combinations of cells and 
vacuum tubes in a single device have 
been proposed. Often these include 
separate elements for both cell and 
tube, or a grid element, serving the 
same function as in the thermionic 
tube, may merely be inserted between 
the electrodes. The advantages of 
such combinations are questionable. 
Where a filament is employed, the 
photoelectric cell has a life which 
terminates when the filament is 

Fig. 3. Mounting for photoelectric 


(Courtesy of Cambridge Instrument Co., 


destroyed, as far as its use in the 
combination is concerned ; otherwise, 
it has been noted, a cell will greatly 
outlast a vacuum tube. The heating 
effect of the filament on the alkali- 
metal surface may also be harmful. 
Furthermore, the current-illumination 
characteristic of a cell is linear from 
the highest to lowest values. The 
current-voltage characteristic of a 
vacuum tube is not linear. This, 
therefore, limits the wider usefulness 
of the cell. An assisting grid in a cell 
may be necessary in certain physical 
research, but the idea is not new; 
Lenard in 1902 was probably the first 
investigator who employed it. There 
are two very significant patents regard- 
ing this structure: Huth, Rosenbaum 
and Loewe (German Pat. 304,325; 
Sept. 28, 1917) and Langmuir (U. S. 
Pat. 1,282,439; Oct. 22, 1918). 

Dr. Robert C. Burt, of Pasadena, 
makes a quartz central-anode cell, but 
the alkali-metal can also be volatilized 
and deposited on the central electrode 
so that the cell can be used for stellar 
photometry as a central-cathode type 
with a saturation point at about 8 

In working with these cells it is 
often desirable to mount them as 
shown in Fig. 3. Here the cell is 
inclosed in a light-tight wooden case 
which is fitted with an iris diaphragm 
and shutter. Thus the size of the light 
beam that falls on the light-sensitive 
cathode can be regulated and also the 
time ' of exposure may be either 
"instantaneous" or the shutter con- 

trolled by tbe bulb, as is the case with 
a photographic camera. 

III. Photovoltaic Cells 

The literature referring to photo- 
voltaic phenomena is less extensive 
than that of either the photoelectric or 
photoconductive effects. Neither has 
the commercial development of cells 
of this sort been undertaken to any 
great extent in spite of the fact that 
there is no doubt of their practical 

In regard to the literature on the 
subject, there seems to be no better 
introduction to it than the interesting 
paper of Carl W. Tucker. 11 Allen 12 
also lists a number of modern ref- 

Tucker describes the typical photo- 
voltaic cell as follows : "If a photo- 
sensitive substance is placed upon two 
metal electrodes which dip into some 
solution, the potential difference be- 
tween these two electrodes, in the 
dark, may be reduced to zero. But if 
one of these electrodes is illuminated 
while the other is darkened, the photo- 
chemical changes, which take place on 
the illuminated surface, may be ex- 
pected to produce a potential differ- 
ence between the exposed and dark- 
ened electrodes. What the magnitude 
of this voltage will be and what will 
be the sign of the charge on the 
illuminated electrode may be expected 
to vary with the nature of the photo- 
sensitive substance and its light- 

Becquerel 13 first prepared and 
named the photovoltaic cell. The 
photovoltaic effect is also known as 
the Becquerel effect. This investiga- 
tor employed silver chloride, bromide, 
and iodide as the light-sensitive ma- 
terial on plates of silver and platinum, 
which were immersed in dilute sul- 
phuric acid. Becquerel observed, as 
Tucker reports, that (1) "the sign of 
the charge on the illuminate electrode 
varied with the thickness of the pho- 
tosensitive material" and that (2) 
"the observed voltage was inconstant 
during the illumination and that its 
value varied with the intensity of the 

Minchin 1 * also investigated the silver 
halides, as well as Wilderman. 15 
More recently, Case 16 prepared cells 
of cuprous oxide on copper plates in 
a solution of 2.5% copper formate 
and 0.4% formic acid. Thus, as far 
as investigations in this field have 
been carried out, it seems that the 
silver halides or copper oxide are the 
most satisfactory materials for prac- 
tical photovoltaic cells. 

One of these cells has been de- 

veloped by Samuel Wein, of New York 
City. It has a semi-cylindrical copper 
plate, which is treated chemically, and 
a lead electrode placed in a bulb con- 
taining a colorless solution (Fig. 4). 
When the copper plate is exposed to 
diffused sunlight, a current of ap- 
proximately 0.5 milliampere will pass 
between the electrodes. Such cells 
can be charged, just as an ordinary 
storage battery is charged, and for a 
time a much larger current flows, al- 
though this effect rarefy lasts longer 
than an hour. However, this charg- 
ing is not at all necessary as the ordi- 
nary current output is large in com- 
parison with the photoelectric cells. 

The chief advantages of these cells 
are that they will operate relays di- 
rectly, that they do not require ex- 
ternal batteries in operation and that 
they do not exhibit the lag noticed in 
photoconductive cells. They will also 
respond to intermittent light compar- 
able to voice frequencies, and hence 
are suitable for photo-telegraphy and 
talking motion pictures. The upward 
frequency is not definitely known — at 
least, not to the writer — and it is thus 
uncertain whether they will respond 
to the wide frequency band required 
for the production of intelligible tele- 
vision signals. However, they are ex- 
cellent for every other purpose. 

10 Jour. Opt. Soc. Am., Vol. 16, p. 177; 
1928: Vol. 17, p. 428; 1928. 

11 "A Study of Photovoltaic Cells" (Jour, 
of Phys. Cliem., Vol. 31, pp. 1357-1380 
Sept.. 1927). 

12 "Photo-electricity," 2nd. ed., 1925. 

13 La Lumi&re, II., 121. 

"Phil. Mag. (5) Vol. 31, p. 207: 1891. 

16 Z. physik. Chem., Vol. 59, pp. 553, 703 ; 

10 Trans. Electrochem. Soo., Vol. 31, p. 
351 ; 1917. 

Fig. 4. The Wein photovoltaic 

(Courtesy of Radiovision Corp.) 

It is also surprising to find that the 
cells are not subject to progressive 
fatigue in so far as rough tests can 
determine. In confirmation of this 
statement, an experimental cell was 
observed at intervals over a period of 
seven or eight months. It does not 
appear that there has been any dimi- 
nution of the photoeurrent in that 

Projection Engineering, September, 1929 

Page hi 



M. C. Batsel, Westinghouse engineer, 
has been appointed to the post of chief 
engineer of RCA Photophone, Inc. Under 
his supervision activities by Photophone in 
recording and reproduction will be con- 


The first regular meeting of the Acousti- 
cal Society of America was held in the 
auditorium of Bell Telephone Laboratories 
in New York City recently. Nearly 300 
attended the meeting, which included elec- 
tion of officers, presentation of papers and 
round table discussions. The enthusiasm 
shown indicates that the new Society will 
have a vigorous and useful life. 

Papers on architectural acoustics were 
numerous during the two-day meeting. 
Architects will be glad to know that there 
was much comment about the desirability 
of co-operation between experimenters as 
well as standardization of test methods. 

The Society includes in its scope work- 
ers in all lines of acoustics. Electrical 
communication, radio, falking pictures and 
musical instruments all have a part in its 
affairs. Physiological aspects of speech 
and audition are, of course, of fundamental 

The following men were elected as 
officers of the Society : President, Harvey 
Fletcher, Bell Telephone Laboratories, Inc., 
New York City ; Vice-President, Vern O. 
Knudsen, University of California, Los 
Angeles ; Secretary, Wallace Waterfall. 
The Celotex Company, Chicago ; Treasurer, 
Charles Fuller Stoddard, American Piano 
Company, New York City. 

Members of the executive council are : 
Paul E. Sabine, Riverbank Laboratories, 
Geneva, Illinois ; J. P. Maxfield, Electrical 
Research Products, Inc., New York City ; 
C. W. Hewlett, General Electric Company, 
Schenectady, New York ; G. R. Anderson, 
University of Toronto, Toronto, Canada : 
Dayton C. Miller, Case School of Applied 
Science, Cleveland, Ohio ; F. R. Watson, 
University of Illinois, Urbana, Illinois. 

It was decided to print the proceedings 
of the Society in full. This volume will be 
a valuable addition to the library of all 
persons interested in acoustics. 

The next meeting was set for Chicago 
on December 13 and 14 of this year. 


The Mella phone Corporation is now 
located in its new headquarters in the 
Keith Albee Theatre Building and factory, 
University Ave., Rochester, N. Y. 

Immediate deliveries are being made by 
the company on the Super Mellaphone. 

Orders just received for Mellaphones are 
being shipped to dealers in Sydney, Aus- 
tralia, Havana, Cuba, Rotterdam, Holland, 
and Calgary. 


With well over 2,000 complete sound- 
on-film and disc reproducers already in- 
stalled in theatres throughout the country, 
Western Electric continues to expand facili- 
ties for production and installation of talk- 
ing picture equipment. It is understood that 
Electrical Research Products, Inc., West- 
ern Electric subsidiary in the sound field, 
now has a service organization capable of 
putting complete installations into thea- 
tres at the rate of 100 a week. 

It is quite likely that the number of 
Western Electric systems operating in 
theatres will mount to the total of 5,000 
by the end of this year. At the rate orders 
are now being placed for the equipments 
and the abilitv of the company to install 
them it is said that the five-thousand mark 
is certain to be reached before 1930. 

The bulk of the orders now being filled 


.T. K. Johnson is now the Philadelphia 
District Sales Representative for Synthane 
Corporation, manufacturer of laminated 
Bakelite products, situated at Oaks, Penn- 
sylvania. Other representatives are J. B. 
Rittenhouse. Chicago ; H. G. Blauvelt. New 
York City ; C. E. White & Company,»Cleve- 


Announcement is made by J. J. Auer- 
baan of the Macy Manufacturing Corp., 
1451 39th St., Brooklyn, N. Y., that in 
order to meet the demand for their ex- 
ponential horns they are enlarging their 
plant, thereby tripling their manufacturing 
capacity. They expect to have this new 
addition in full production by the middle 
of September. 


With the recent development of a novel 
combination scanning drum and selector 
shutter disk by its engineering staff, re- 
sulting in a simpler, more economical, and 
far more practical scanning system, the 
Jenkins Television Corporation of Jersey 

called for installation of the dual system 
equipments, with the added feature of a 
non-synchronous attachment included in a 
high percentage of the new business now 
begin written by the company. The de- 
mand for non-synchronous alone has fallen 
off to such an extent that this unit of the 
line has become a negligible quantity, it is 


Formerly of Station WOR, Newark, N. J., 
where he handled program and production 
work, J. S. Carlile has been announced as 
head of the newly created radio depart- 
ment of Paramount. The department is 
handling the company's radio plans now 
being formulated and is an outgrowth of 
the recent purchase of a half interest in 
the Columbia Broadcasting System by 
Paramount. Mr. Carlile has also acted as 
guest announcer for the Columbia System 
and has written a number of programs for 
presentation over the air. 


The Tono-O-Graph sound motion picture 
reproducing machine, is now being manu- 
factured in quantity production for thea- 
tre installations, Jt is announced by the 
North American Sound and Talking Picture 
Equipment Corp., New York, whose factory 
is located at Long Island City. Prices of 
the reproducing machine are placed at 
$1,800 and $2,500. Installation, to take 
three hours, is made free of charge, the 
company charging only for the wiring. 


The Fox Film Corp. is pushing work on 
its new wide film process and it is under- 
stood that the first public showing of 
Widescope will be given early in Septem- 
ber. Special projectors for use with Wide- 
scope have been built by the International 
Projector Corp., which company is under- 
stood to have cooperated with Fox in the 
development of the process. 

Widescope is the third entry in the wide 
film derby, both RCA and Paramount hav- 
ing already demonstrated their processes 
—the Spoor-Berggren and Magna-film sys- 
tems, respectively. 


City, N. J., now announces the mass pro- 
duction of television apparatus. 

"Although we have been in production 
on experimental television equipment for 
six months past," states James W. Garside, 
President of the Jenkins Television Cor- 
poration, "we have withheld mass produc- 
tion of market models until we could be 
positive of our grounds. Our earlier 
models were too elaborate and costly for 
use in the average home, while the results 
left much to be desired. Therefore, our 
production until now consisted of sample 
televisors for use in checking up the effi- 
ciency of our television transmitters at 
Jersey City and Washington, under typical 
receiving conditions. 

"With our latest development, we have 
evolved a remarkably simple, inexpensive, 
and highly practical televisor, which can 
be readily manufactured at a reasonable 
cost. The new Jenkins televisor will per- 
mit of receiving either plain black-and- 
pink radiomovies or full halftone pictures, 
with good detail and illumination within 
the limitations of our present 48-line sys- 
tem. Should we find it advisable to go to 
60 or more lines, based on our present 
experiments and developments, the Jenkins 
televisors can be readily changed over to 
accommodate additional lines and finer 


The Bakelite Corporation have selected 
seven tracts, embracing over 130 acres, in 
Middlesex, N. J. for their own plant. The 
properties border on the Reading and the 
Lehigh Valley Railroads. 


L. C. Porter, president of the Society of 
Motion Picture Engineers, announces that 
the board of governors has decided to hold 
the next meeting of the society in Toronto, 
October 7 to 10. inclusive. 

Canadian and other members of the 
S M P E have been making an insistant de- 
mand for a convention to be held in 
Canada, as none has been there since the 
one in Ottawa in 1923. 

As the spring meeting, held in New York 
last May, was highly successful from every 
standpoint, greatly increasing the member- 
ship and making the industry better ac- 
quainted with the activities of the society, 
it is believed that the attendance will be 
very large at the coming Toronto meeting. 


It is reported that a new German sound 
reproducing equipment is to be brought on 
the market. It is to be constructed accord- 
ing to the Lignose-Breusing system and to 
use T. D. K. amplifiers. The recent ruling 
of Berlin courts against Western Electric in 
connection with the use of these amplifiers 
is supposed not to apply to the proposed 
apparatus, as an agreement exists between 
the promoters and the electric concern of 
Felten-Guilleaume of Burenberg, which be- 
longs to the exploiting syndicate of the 
Lieben patents, in the same way as does 

The new equipment is to he a disc system 
and is expected to cost from 6,500 marks to 
9,500 marks, according to the size of the 
house to be wired. 


The American Seating Company is offer- 
ing a special service to theatres in connec- 
tion with its supplying of theatre chairs. 
Advice on acoustical problems will be given 
by its engineers in consultation with Dr. 
F. R. Watson, acoustical expert of the 
University of Illinois. 

Page 48 

Projection Engineering, September, 1929 


The Earl B. Hough Co. of Chicago, Illi- 
nois, makers of the Hough Organ Lift, an- 
nounce a new automatic sound picture 
horn lift. The problem of what to do with 
horns while a stage act was on was only 
partially solved with the introduction of 
movable horn towers which permitted the 
rolling-off of the horns into the wings. 
The one objection of these towers was that 
they required much valuable stage space. 

The Hough horn lift is installed under 
the stage floor and is operated automati- 
cally much in the same fashion as is an 
organ lift. The horn lift is contained with 
in a ceiling height of 8 feet below the 
stage and has an upward travel of 15 feet 
or more, as required. It is powered by a 
1% horsepower motor, driving a cable con- 
suming drum through a ball-bearing steel 
and bronze worm gearing and operates in 
a dust-proof oil bath. The raising or low- 
ering operation, which is silent, requires 45 

The lift is operated from a push-button 
located on the stage switchboard, with the 
lift, when traveling either up or down, 
stopping automatically at the predeter- 
mined end of travel. The National The- 
atre Supply Co. will furnish full details of 
this unit. 


Full details on the two new Pacent 
Junior models for houses up to 500 seats 
were released recently by the Pacent Re- 
producer Corporation. Pacent, in issuing 
the statement, promised the small exhibitor 
machines which deliver the highest quality 
and performance. The new machines com- 
bine a number of new features. 

There are two new Pacent models for 
houses up to 500 seats. The Type 500 
DDA is for synchronous disc reproduction, 
and sells for $1,500. It has full double- 
channel amplification with a reserve ampli- 
fier for every amplifier used to run a show. 
No batteries are used in the operation 
of the system. The amplifiers operate 
direct from any 110-volt, 60-cycle a-c. 
source. Other features found in the new 
Junior model 500 DDA are constant speed 
motors, mechanical gear drive, and a new 
type of pickup which tracks all records 
perfectly and has a remarkable coverage 
of the frequency range. 

The latest type of dynamic speaker is 
used in both the new Pacent models. This 
type of speaker, especially developed for 
small theatres, is said to give unusual 
power, with a large reserve to bring out 
the full effect of all programs. 

The second of the new Pacent machines 
is known as the Type 500 FDA. It com- 
bines synchronous disc and sound on film 
reproduction. The price of this model, for 
houses up to 500 seats is $2,500 for both 
disc and sound on film. The features of 
the disc system are the same as those for 
the Type 500 DDA disc system, including 
full double-channel amplification, new type 
pickup and mechanical gear drive. 

The sound-on-film section of the new 
Type 500 FDA combines several new and 
highly interesting features. Both the 
variable area and variable density methods 
are played with equal efficiency. The 
sound-on-film section is extremely simple 
to operate, due to special designed features. 
When disc is played it is not necessary to 
thread through the sound-on-film section. 
A specially designed optical system is em- 
ployed, which with the special photoelectric 
cell gives the highest quality of reproduc- 
tion by the sound-on-film method. A new 
feature in sound-on film section is found 
in the periscope through which the pro- 
jectionist makes a complete, quick check 
on sound-on-film operation. 

The two Pacent models Type 2 MDA 
and TYPE 4 MDA for houses up to 4,000 
seats are continued as regular items. No 
nrice change in these models has been 
made and none is contemplated according 
to the Pacent Corporation. 


The salient feature of the Presto Record- 
ing Machine is its vibrationless construc- 
tion accomplished through the simple ex- 
pedient of a belt drive separating the power 
unit from the recording head. 

By this simple and at the same time 
thoroughly mechanical construction th« 
need of expensive filtering devices so neces- 
sary in geared constructions — and at best 
inefficient — is at once eliminated and there 
is provided a smooth, even, perfectly regu- 
lar transmission to the recording head by 
which the slightest vestige of vibration is 
eliminated at the essential point. 

The machine is available for regular 
recording at 80 r. p. m. or 33 1/3 r. p. m. 
for synchronized picture work. The change 
over is practically instantaneous. 

The belt drive for synchronized work is 
of such design and- construction as to in- 
sure positively the established ratio and 
to maintain such ratio under any and all 

In fact, the construction is such as to 
make the machine almost universal inas- 
much as any desired feed can be made 
available by the simple substitution of a 
pulley on the recording end. 

A vital constructional feature is the turn- 
table tapered bearing which is self-aligning 
and automatically adjustable to wear with- 
out the need of end-thrust take-up. The 
bearing is a fit when made, remains a fit 
and there is no possibility of any play 

A convenient feature is a simple cam 
means for establishing a positive cutting 
starting point. The cutter point is 
dropped on the wax at the desired start- 
ing point and the simple operation of set- 
ting a stop against the cam face automati- 
cally produces the starting groove and the 
feed then proceeds at the predetermined 
rate. For straight recording a hand lever 
operation cuts the spiral groove at the end 
of the record. 

A play-back is provided on the feed slide 
whereby immediate testing can be made 
without removing or disturbing the cut- 
ter head, means being provided for en- 
gaging or disengaging either the cutter or 
the play-back. 

The machine is designed and built on the 
unit-construction plan, is portable in the 
most practicable sense and is of precision 
specifications to a degree that insures per- 

fect cutting for both straight and syn- 
chronized recording work. 

The machine is the latest development 
of the Presto Machine Products Co., 70 
Washington St., Brooklyn, N. Y., which 
concern has specialized in the production 
of sound reproducing devices for the past 
thirteen years. 


An ingenious combination of scanning 
drum and selector shutter has just been 
demonstrated by the Jenkins Television 
Corporation engineers. The new arrange- 
ment, which takes the place of the Jen- 
kins scanning drum with light-conducting 
rods and four-plate neon glow lamp, is far 
simpler, cheaper and more efficient in mat- 
ters of detail and illumination. In fact, 
not only are the silhouette or Jenkins 
radiomovies received with crisp, sharp, 
sparkling black-and-pink definition, but 
halftone pictures are also handled by the 
same scanning mechanism with excellent 
results. With experimental transmissions 
of a close-up film of a girl by the Jenkins 
W2XCR station, the new scanning mech- 
anism can reproduce the animated pictures 
with sufficient detail so that the features 
are readily identified by the lookers-in. 
There is also a considerable increase in 
illumination, due to the use of a stand- 
ard neon lamp with large plates, instead 
of the former small plates of the four-plate 
neon lamp. With the elimination of the 
revolving contact switch gear for flashing 
the multiple plates in proper turn, the 
present mechanism presents a minimum of 
noise in operation. 

The main point about this new Jenkins 
development, however, is that a scanner 
can be produced at a relatively low cost. 
With the elimination of the elaborate 
scanning drum with light-conducting rods 
and multiple-plate neon lamp, the equip- 
ment is reduced to simplest and most eco- 
nomical terms, yet the performance is re- 
markably improved. The use of a novel 
selector shutter in combination with a 
small scanning drum, so that the drum 
rotates four times in flashing each 48-line 
picture, results in retaining the compact 
dimensions for which the Jenkins tech- 
nique is noted. 

Cam for Starting Line fSf < ' ' / 

mV^Feed Nut Lever 

Synchronous Motor 33 Vz R.P.M. 

For 80 R.P.M. Recording Use 
Round Belt— 

Perforated^ Belt 
for Synchronizf 

m Cam era 

Explanatory illustration of the Presto recording machine. 

Projection Engineering, September, 1929 

/'a«7e 4.9 


Page 50 

Projection Engineering, September, 1929 


The Burt Synchronous Reproducer illus- 
trated is one of the simplest reproducers of 
talking motion pictures both film and disk 
which has appeared on the market. 

Synchronous Motor Drive (110 or 220 
volts, 50 or 60 cycles). Prevents variation 
in speed from variation in line voltage, or 
projection load. 

The Super Cells used require only two 
stages in head amplifier, hence less distor- 

Ease of Threading. When running disk 
or silent, the Sound-on-Pilm unit is not 
threaded. Sound-on-Film threads as easily 
as through a Powers gate. 

Turn Table is Accessible, being up high 
at the side of the machine. 

Easy to Install. Installation can be made 
by the ordinary operator, and wire man. 

Projector Head is driven by its main 
drive gear and is not required to drive any 
part of the sound equipment. 

Only Three Shafts: (1) Motor Drive, 
(2) Sound Film Shaft, (3) Disk Table 

Variable Speed can be used for making 
schedule by driving the head off the Powers 
Motor, when running silent. Change from 
synchronous drive to variable speed drive 
requires about ten seconds. 

No Vniversals — No flexible couplings, flex- 
ible shafts, or long unsupported shafts are 
used, as these produce tremolo. 

Fire Hazard is Decreased by use of this 
equipment. Failure of take-up does not 
cause film to pile up in light. 

The photoelectric cells used have such a 
high output that only two stages of am- 
plification are required in the head ampli- 
fier which feeds through the Fader directly 
into the power amplifier which may be any 
standard make of three-stage power ampli- 
fier. Two photoelectric cells are supplied 
with each head in one case, and in the event 
that one cell ceases to function the other 
may be put into operation by simply rotat- 
ing the cell case one-half turn. No ampli- 
fier tubes are used in the cell case or on 
the machine itself. The wires from the 
photoelectric cells are brought out to a jack 
which plugs into the head amplifier. An- 
other jack on the disk pickup arm plugs 
into the same head amplifier and there- 
after control is had by means of the switch 
on top of the head amplifier. When this 
switch is in a vertical position everything 
is "off" ; when switched to the left the 
disk is connected to the Fader ; when 
switched to the right the head amplifier 
filaments are lighted and ^he Sound-on-Film 
pick-up is connected to the Fader. 

Manufactured by R. C. Burt Scientific 
Laboratories. 900-904 E. California Street, 
Pasadena, Calif. 


The new Jensen Concert Dynamic is to 
be built in four types for operation from 
110 volt a-c. 110 volt d-c, 220 volt d-c. and 
6 volt d-c. 

Jensen "Concert" Dynamic 

The top price is $35 for the unit for 
operation from 110 volt a-c. This unit is 
equipped with a dry rectifier system and 
operates without perceptible hum from the 
alternating current. The models for opera- 
tion from d-c will carry a list of $27.50. 

The new Concert speaker is to be offered 
also in the Jensen Imperial Cabinet which 
was announced earlier in the year. 
Equipped with the Concert Dynamic unit, 
the list prices have been set at $80 with 
the a-c. unit, and $72.50 with any one of 
the three d-c. units. 


The Ellis Electrical Laboratory, 333 
West Madison St., Chicago, have intro- 
duced a new two-button stretched dia- 
phragm carbon granule microphone, known 
as Model No. 29. The carbon hiss which 
is characteristic of so many microphones 
is at an exceptionally low level. This mi- 
crophone has no harmonics of its own and 
will give no distortion. It is of a rigid 
three-pillar construction and will therefore 
withstand rough handling, without losing 
its fine adjustment. 

A feature of this microphone is that suf- 
ficient sensitivity is obtainable for all prac- 
tical purposes with a consumption of only 
5 ma. at 3 volts. A factor of safety is 
provided by allowing 10 ma. to be used 
on each button without danger of burn- 
out. This sensitivity is obtained without 
minimizing the carbon content or creating 
diaphragm resonance. Sufficient carbon is 
used to insure durability. 

Finished in either nickel or statuary 
bronze. Diameter, 3.4 inches ; overall 
thickness, 1.5 inches. Can be mounted in 
any standard stand. The list price of the 
Ellis Model No. 29 microphone is $70. 


The American Silversheet Co., of 800 
Beaumont St., St. Louis, Mo., have per- 
fected a new sound screen which is con- 
structed of a specially jelled pyroxylin 
process which impregnates the surface 
into the material in such manner that in 
addition to the fact that this screen can 
be washed it also becomes scuff-proof. 

The screen is constructed with specially 
designed even-staggered perforations, for 
the passage of sound, but the perforations 
in no way interfere with the projected 

The Burt Reproducer for Talking 
Motion Pictures 


The Mellaphone Corp. of Rochester, 
N. Y., makers of the Mellaphone sound 
picture apparatus, is now offering a speedo- 
meter for motion picture projection work. 

This new speedometer is guaranteed as 
to workmanship, durability and accuracy 
and is warranted to give complete satis- 
faction. The price of this new speedo- 
meter is $20 complete. 

Mellaphone is ready to make immediate 
quantity deliveries of the speedometer. 


A giant dynamic loudspeaker unit of 
radically new design and very high effi- 
ciency has just been announced by the Am- 
plion Corporation of America. The new 
unit is known as "type AA-102 — Improved 
Giant Dynamic" and displaces the older 
"AC-100" model. 

The magnetic field of the AA-102 has 
been reduced to two-thirds the size of the 
AC-100, although the flux density has been 
increased by 7 per cent. The weight of 
the unit has been decreased from twenty 
pounds to only fifteen pounds. The use of 
a special magnetic metal alloy makes pos- 
sible this lighter weight and stronger mag- 
netic field. 

An important new feature of the "Im- 
proved Amplion Giant Dynamic" unit is 
the composite diaphragm. The composite 
construction provides a double sound cham- 
ber above the diaphragm, which produces 
remarkable tone separation. The center of 
the diaphragm is convex, giving greater 
strength. Vanes radiate outward towards 
the periphery of the diaphragm. These 
furnish additional re-enforcement, prevent- 
ing ripples which might create extraneous 
noises. The diaphragm is made of dura- 
luminum, for extreme lightness. The voice 
coil is wound with fine copper wire and 
has an impedance of 8% ohms. Specially 
prepared flexible leads are used to bring 
connections to the binding posts, thus 
avoiding the possibility of coil breakage. 

The over-all dimensions of the unit are 
5% inches in height by 6 inches in diam- 
eter. The lower portion of the unit is only 
4% inches in diameter. 

The new Am- 
plion "Giant 
Dynamic" unit, 
for theatre 


The type AA-102 Amplion unit has been 
developed especially for talking motion pic- 
ture use, although it can be used to great 
advantage for all high volume public ad- 
dress work. It requires a field supply of 
1.6 amperes at 6 volts d-c. For theatre 
work the unit is generally used with an 
Amplion M-10 exponential horn, having an 
air column ten feet in length. The new 
unit, in combination with the air-column 
horn has a wide response range and enor- 
mous volume with super-fine tone quality. 


The Super-Power Clarostat is a heavy- 
duty adjustable resistor intended for all 
manner of applications calling for a pre- 
cise resistance value. This device is based 
on the well-known Clarostat compression 
principle of obtaining stepless and noise- 
less resistance that remains set at any 
value desired. Thus the Super-Power 
Clarostat is at once a variable resistance 
when it is necessary to try different values, 
and a fixed resistance when the proper 
value has been found by actual test. 

For the various applications in radio 
as well as in electrical work, the Super- 
Power Clarostat is furnished in three re- 
sistance ranges, namely : 

Filament Range % — 10 ohms 

Low Range 25 — 50 ohms 

Universal Range . . . 100 — 100,000 ohms 

This device is built for heavy-duty serv- 
ice. It is capable of withstanding high 
temperatures when dissipating up to its 

Super-Power Clarostat. 

Projection Engineering, September, 1929 

Page 51 


Since the advent of dry metallic rectifiers Elkon has 
always led in perfection of design and record of per- 
formance. Many of the leading manufacturers have 
brought their rectifier problems to Elkon for solution. 

The signal success of Elkon rectifiers in the "As! 1 Elim- 
inator and battery charging fields was followed by 
outstanding achievements with low voltage rectifiers 
for dynamic and other moving coil speakers. 

Again, this year, looking ahead and interpreting the 
need, Elkon introduced the new high voltage recti- 
fiers which eliminate the power transformer in 
dynamic speakers and others of moving coil type. 

Whatever may be your problem of rectification, 
Elkon engineers will be glad to co-operate with you 
in working out its solution. 

ELKON, Inc. 

Division of P. R. Aiallory & Co., Inc. 



Page 52 

Projection Engineering, September, 1929 

maximum capacity of 250 watts. It is 
provided with a long shaft and special 
bracket, so as to be mounted clear of the 
panel for proper air circulation, or again 
for mounting on thick slate panel. Ideal 
as a heavy-duty line control, variable speed 
motor control, plate voltage control for 
transmitters, field control for shunt type 
generator, and so on. Finished in nickel. 
Mica and asbestos insulation. Handy 
bakelite knob. Sturdy and wearproof. 


A new sound installation designed for 
theatres up to 500 seats capacity and to 
cost not more than $2,995 installed will 
soon be placed on the market by RCA- 
Photophone. The new model will be a 
dual-system unit, for reproduction of both 
disc and sound-on-film recording. 


The X-Core marks a further improve- 
ment in Magnavox Speakers. It is a very 
definite refinement and one that provides a 
positive alignment of the moving coil in 
the air gap. 

There are two main divisions of the 
speaker assembly. The cone head and the 
field coil frame assembly. The cone bead 
includes the cone housing, the paper, cone, 
the moving coil and the X-Core. The field 
coil frame assembly includes the field coil, 
the heavy steel case enclosing the field 
coil, the main core, the input transformer 
and the speaker base. 

The moving coil, or driving unit is 
rigidly and directly attached to the cone, 
and delicately suspended in the strong 
magnetic field produced by the field coil 
and transmitted by the steel case and the 
cores. Bakelite, proved to be the best be- 
cause of its durability aud its resilience, is 
used to suspend the moving coil. This 
coil is fastened to the cone with a special 
cement and rigidly clamped with the 
aluminum retaining ring. The flexible mov- 
ing coil leads are completely insulated and 
very sturdy. The air gap in which the 
moving coil oscillates is between the 
X-Core and the outer pole and as the 
X-Core is pressed into a bearing in the 
outer pole the air gap must be always 

This construction simplifies conehead 
ajpemblies, as the X-Core is included in 
tire conehead and the screw connecting 
the main cone and the X-Core is used only 
to hold the two in magnetic contact. It 
is evident that coneheads can be replaced 
with absolutely no danger of the coil rub- 
bing in the gap. It is a distinct advantage 
to have the conehead removable. It facili- 
tates assembly as well as it does replace- 
ment or repair. This is an exclusive 
Magnavox feature, and with the develop- 
ment of the X-Core makes it absolutely 
positive and sturdy. 


Powrad, Inc., of Brooklyn, New York, 
are marketing a complete line of by-pass 
and filter condenser blocks housed in metal 
cans with mounting and soldering lugs 
both in standard blocks and to manufac- 
turers' specifications. 

These condensers are conservatively rated 
and guaranteed in capacity from — 5% to 

A unique method of impregnation ac- 
quired through six years' of skill and experi- 
ence in the manufacture of paper con- 
densers have led to the production of an 
exceedingly rugged product noted for its 
remarkable working strength and high in- 
sulation resistance. 


non-inductive filter con- 


Amplifier racks and control panel equip- 
ment for centralized use in theatres, schools, 
auditoriums, stadiums and other places 
where music or voice is to be "piped" over 
large areas, has just been introduced by 
the Radio Receptor Coznpany of New York 
City. This equipment is of the panel or 
vertical rack type, although made up essen- 
tially of the well-known powerizer units. 
In the case of the two-channel assembly, it 
stands 6 feet high by 20 inches wide, com- 
prises six panels, and weighs 200 pounds 

The two-channel amplifier assembly, which 
is certain to be the most popular for 
most installations, comprises 
a PXP-250 powerizer, made 
up of two units, for each chan- 
nel. Thus the panel assemblv 
represents a monitoring loud- 
speaker and distortion meter 
for the top panel ; a switch and 
pilot light for the PXP-250 or 
power output unit, representing 
the second panel : a switch and 
pilot light for the voltage amp- 
lifier or PXP-171 unit, repre- 
senting the third panel ; the 
fourth panel contains the main 
switch and throw-over switch 
from one channel to the other, 
the a-c field switch for the 
dynamic speakers and a throw- 
over input switch from synch- 
ronous to non-synchronous : the 
fifth contains the second PXP- 
171 powerizer and its switch : 
and the sixth contains the 
PXP-250 and its switch. The 
assembly is so arranged that 

-:■:::-. ■.. .■.--■ ■■■■.-:■. -A 

iiiiiiiillllillliiiiiiiiiiiinii iiiiiiiii:iiii!iii[iii!i[iiiiiiiiiiiiiiiiui milium 

Right: New Powerizer two- 
channel amplifier, containing 
a distortion meter, a monitor 
ing loud-speaker and all the 
necessary control equipment. 

any of the complete units with panel may 
be removed and another unit substituted, 
such as a monitor, or a radio set with amp- 
lifier and microphone panel, which, of 
course, would take care of the microphone 
meter and switch. The power units are 
the standard powerizers arranged for 
bracket mounting. All audio wiring Is 
carefully shielded so that these units are 
found very quiet in operation. 


Wright-DeCoster, Inc., of St. Paul. Minn- 
are in production on their new dynamic 

The field coil of this dynamic speaker 
contains nearly fifteen pounds of wire, 
which, in combination with an extremely 

Wright-De Coster dynamic speaker 

low reluctance magnetic path provides a 
high degree of efficiency. Notwithstanding 
the fact that only nine watts are necessary 
for field excitation, and the air gap is some- 
what larger than standard practice, there 
is sufficient sensitivity to produce an out- 
put, on a single 171-type power tube which 
is usually possible only with a 210-type 

The unit will stand exceptionally high 
powers, having been used successfully on 
amplifiers supplying as high as 45 watts 
of speech energy. Due to special construc- 
tion of the voice coil, there is little possi- 
bility of voltage breakdown between layers. 

There is usually no equalizer or cut-off 
filter necessary except on an amplifier in 
which there is a prevalence of harmonics 
of very bad wavelength distortion. 

Prices on the speakers range from $52 
to $100, with and without cabinets and in 
both 6-volt d-c. and 110-volt a-c. types. 


Wright-DeCoster, Inc., of St. Paul, Minn., 
have also introduced a new Tone Modulator 
which is employed for increasing or de- 
creasing the high and middle registers of 

Details of the Magnavox X- 

Core Speaker, a recent new 


Projection Engineering, September, 1929 

Page 53 

A cure for Line Voltage Ills! 

NO longer is it necessary for your 
talking picture equipment to be 
at the mercy of fluctuating line volt- 
age. You can be absolutely indepen- 
dent of all fluctuations by including 
the • 




The giant variable re- 
sistor, which, in several 
turns of the knob, pro- 
vides a wide resistance 
range. Handles 250 
watts. Available in 
14-10, 25-500, and 
200-100,000 ohm 

Provided with extra 
long nipple for mount- 
ing on slate or marble 
panel, and with special 
bracket for mounting 
on bakelite panel. Also 
ideal as variable speed 
motor control and gen- 
erator field control. 

\\7 O ¥ TH C" regarding this and other CLAROSTAT devices which, 
» » -1^ * * *-* having set a high mark in radio, are now available for the 
peculiar requirements of picture projection and sound reproduction. 


Specialists in Radio Aids 
296 N. 6th St. -:- Brooklyn, N. Y. 

Page 54 

Projection Engineering, September, 1929 

the musical scale. This can be done at 
the will of the operator and without dis- 
turbing the lower middle and bass tones. 

Wright-De Coster dynamic speaker 

The Tone Modulator is designed to be 
connected between the phonograph pickup 
and the input of the audio amplifier. It 
readily lends itself for use in connection 
with sound equipment in theatres. 

The Tone Modulator is priced at $7.50. 


The Foto-Voice Synchronizing Unit as 
herein illustrated is a sturdily constructed 
iron stand supported by three adjustable 
iron legs, and on which is mounted a 
unique worm reduction gear and stabilizing 
assembly. On this a 16-inch balanced 
aluminum turntable is rotated by means ot 
a direct drive pinion shaft — the possibility 
of record slippage being eliminated by a 
depression machined in its center and a 
nickeled weight placed on the record at 
this point. The tone arm is of mahogany 
and swung in carefully machined bushings 
for perfect freedom of movement — a high 
grade make of electric pickup is employed 
— the assembly being properly balanced for 
maximum reproduction results. 

The driving medium is through a spe- 
cially constructed adjustable shaft, which 
in turn is driven by a simple gear and 
bracket attachment at the projector. The 
complete unit requires only twenty inches 
of floor space and may be placed to either 
side of or under the rear of the projector 
lamp house. 

The Booth control panel provides for 
switching from one turntable to the other 
and from the booth to the Non-Synchro- 
nous Console, with a fader which permits 
absolute control of volume to the amplifier 
input. An auxiliary changeover switch is 
also supplied for location wherever most 
convenient to the operator. 

The Foto-Voice Non-Synchronous Con- 
sole is a finely finished cabinet measuring 
17" x 32" by 30" high — the front panel of 
this cabinet is hinged to open for greater 
convenience in operating and the top is ar- 
ranged to be entirely removable if so de- 
sired. Two Bodine non-interference turn- 
table motors are employed, each operated 
by individual switches that are mounted 
on a small bakelite panel which also car- 
ries instant changeover and fader control 
and effect button. 

The Booth Monitor Horn is a 7%-inch 
cone magnetic speaker mounted in a 12- 
inch cabinet, and is equipped with indi- 
vidual volume control. 

The Amplifier is an entirely a-c-operated 
unit of well-known manufacture, and is 





capable of properly reproducing voice and 
music in any degree of volume required. 

The Speakers are of the dynamic a-c- 
operated cone type, and are attached to 
two specially designed horn units with a 
30-inch bell opening. 

Manufactured by The Foto Voice Com- 
pany, 817-19 Granby St., Norfolk, Va. 


The new model Universal Broadcast Sta- 
tion Microphone is now available through 
the New York and Chicago offices of the 
Gotham Engineering and Sales Co., or from 
the Universal Microphone Co., Inglewood, 
Calif. This is a superior two-button unit 
with solid back, stretched duralumin dia- 
phragm and gold contact surfaces. The 
curve of response is unusually flat from 
30 to 10,000 cycles, and the absence of 
bothersome "hiss" is notable. It can be 
supplied complete as shown in the photo- 
graph, equipped with ring desk mount, 
covers, and cord, or the microphones alone 
can be procured. ,f 


'KK" two-button micro- 

This microphone is ideal for use in broad- 
cast studios, public address work, announce- 
ments in connection with talking movie in- 
stallations, or wherever the most perfect 
pick-up of the carbon granule type is re- 
quired. The unit alone lists at $75.00, or 
complete with ring desk mount, covers, 
and cord, as shown, at $98.50. 

The new "Foto-Voice" synchroniz- 
ing unit attached to standard 


New models offered by The Rola Com- 
pany include the Rola electrodynamic units 
for installation by manufacturer or dealer 
in cabinet radio sets and electric phono- 
graphs, as well as the Rola units in talk- 
ing picture installations, public-address and 
school systems. They also include three 
Rola cabinet loudspeakers for use with 
table receiving sets. 

In its display the Company is presenting 
for the first time two new Rola electro- 
dynamic units and is also introducing 
further refinements and improvements in its 
"J" line of electrodynamic reproducers. 

The new Rola electrodynamics have a 
high output efficiency, obtained by the use 
of relatively high flux densities in the air 
gap. High flux densities are obtained with- 
out increase of field energizing power, 
through the use of very short air gap 
distances. The short, precision air-gap is 
made practical by a highly refined moving 
coil structure, together with extreme ac- 
curacy in the spacing of the pole pieces. 

Another improvement is the ventilating 
of the field winding which minimizes tem- 
perature changes. The new Rola ventilnted 
construction e'iminates dead-air insulating 
areas around the windings and results in a 
substantial reduction in operating tempera- 

The removable center-pole nose piece — an 
exclusive Rola feature which enables easy 
elimination of any magnetic particles which 
misrht enter the air gap — has been retained. 
The new "J" series of electrodynamic 
units with 7%-inch cones and adjustable 
center pole tip, have been further improved 
and refined. Chief among the new features 
is the laminated bakelite spider support, 
ventilated field coil and more effective slot 
openings behind the cone. 

Included in the "J" series are the Model 
"J-90" for field excitation from standard 
power-pack. The series also includes the 
Model J-110, a complete electrodynamic 
unit for light-socket operation with all 
sets and amplifiers. Other Rola elec- 
trodynamic units for manufacturers or 
dealers are wound to meet any voltage 

New Rola "Concert' 


current ratio and for use with any power 
pack circuit. 

In addition to the above units the Rola 
Company also provides the Rola Cabinet 
Loudspeaker Model 30-J — equipped for light- 
socket operation with any table receiving 

The new "C" or Concert Series electro- 
dynamic units are similar in all respects to 
the "J" types except for their 9-inch cone 
diameter. This increased cone size gives 
somewhat greater power capacity and is 
adapted particularly well to amplifiers 
using 245 tubes in push-pull combination. 

The new "R", or Auditorium electro- 
dynamic unit, has a cone diameter of 12 
inches. It possesses a magnetic field struc- 
ture of great size and power und uses the 
full output of a type 280 rectifier tube. 

Among the Rola electromagnetic loud- 
speakers are the Rola Model 20 cabinet 
speaker — attractive in design and of estab- 
lished popularity. The Rola Model 15 

New Rola "Auditorium' 


equipped with the same unit as the Model 
20, furnishes high quality performance at 
moderate cost. The Rola Model M is the 
complete electromagnetic unit as installed 
in the Rola Models 15 and 20. 


A new phonograph pickup has been an- 
nounced by the Best Manufacturing Com- 
pany of Irvington, N. J., manufacturers 
of the famous BBL, Motor. 

One of the serious objections to pick- 
ups has been the damage they do to thi? 
records. When one first looks at the Best 
Theatre Pickup one would think its large 
size and tremendous weight would wear out 
the records even quicker than the other 

The Theatre Pickup, however, is so fine- 
ly counterbalanced that just enough weight 
bears on the record for the needle to track 

Projection Engineering, September, 1929 

Page 55 



(The subscription 
rate for individual 
subscribers is $2.00 a 

Will you not cooper- \ ^U^ eSS . 
ate with us by classify- W 
ing subscriptions sent in 
as follows: 

(M) Manufacturer 

(Please check "M" if yon are an execu- 
tive, purchasing agent, production mana- 
ger, service manager, plant superintendent 
or foreman.) 

(E) Engineer 

(T) Technician 
(D) Distributor or 

(P) Projectionist 
(A) Theatre or Theatre 


Page 56 

Projection Engineering, September, 1929 

core upon 

The new Best theatre pickup. 

perfectly. That is true of high and low 

The idea of the Best engineers was to 
design a pick-up which would give the 
general public the benefit of a pick-up which 
would be in every way comparable with 
those now used in the theatres and which 
cost well over $200. The Best Theatre 
Pick-up has a response curve which is re- 
markably close to the high priced, oil- 
floated types it is claimed. 

Needle scratch is appreciably less end 
record life is thereby greatly increased. 


The General Amplifier Company, 27 Com- 
mercial Avenue, Cambridge, Mass., has in- 
troduced three new power amplifiers : 
Models GA 10, GA 20 and GA 30. 

The GA 10 is a two-stage amplifier em- 
ploying one 227-type tube, one 230 and a 
281. It will deliver approximately 4 watts 
of undistorted energy to the speaker. 

The GA 10 amplifier lists for S88. 

The GA 20 is a three-stage amplifier 
employing two 250s, two 226s, two 281s 
and a 227. It will deliver approximately 
■14 watts to the speaker. 

The GA 20 lists at $225. 

The GA 30 is a three-stage amplifier 
employing two 250s, two 281s and two 
227s. It will deliver approximately 12 
watts to the speaker. 

The price of the GA 30 is $175. 

All three amplifiers are designed for use 
with either a magnetic or a dynamic 
speaker. No output devices are required. 

Each amplifier employs filters in the 
plate and grid circuits of the tubes, thus 
isolating the signal voltage from the plate 

The General Amplifier Company is in a 
position to manufacture amplifiers to meet 
special requirements. 


The Thordarson Electric Manufacturing 
Co., of Chicago, are marketing a new type 
of audio transformer of small dimensions, 
known as the R-260. Though this trans- 
former measures only 2 by 214 inches, it 
has excellent frequency characteristics. Its 
fine performance is partly attributable to 

the Thordarson "DX Metal" 
which the coils are wound. 

It is claimed that the R-260 transformer 
is entirely devoid of resonance peaks and 
provides excellent performance over the 
entire audible band. 

The list price of the R-260 transformer 
is $5. 

Thordarson R-260 Audio 


The Amplion Microphone is of an unusual 
design. The design was the result of the 
efforts of the engineers to produce a micro- 
phone that could be relied upon regardless 
of the weather or the nature of the usage. 
The result was a microphone that did not 
pack during operation and the granular 
hiss was reduced to a negligible quantity. 
No metal diaphragm is used in its construc- 
tion. There are no carbon buttons. These 
items were eliminated by the engineers 
forming a narrow channel-way across the 
face of the microphone. This channel-way 
is formed with moulded bakelite. It is 3/16" 
deep, iy 2 " wide, and 2%" long. At each end 
of the channel-way is a carbon electrode and 
the rest of it is filled with a special granu- 
lated carbon obtainable only in Europe. 
These carbon granules are held in position 
by a very thin rubber membrane. All 
sound impinges on this membrane, creat- 
ing a displacement of the carbon granules, 
said displacement producing a fluctuation 
of the electric current which flows through 
them from one carbon electrode to the 
other. This variation is in direct propor- 
tion to the volume of the sound impact and 
in absolute synchronism with its frequency. 

This microphone will not blast and will 
stand up under extremely rough usage. It 
requires approximately 25 volts d-c. for 
maximum operation, due to the fact that it 
has an internal resistance of 500 ohms. 
At this voltage, a current of 60 milli- 
amperes flows through the microphone, mak- 
ing possible an extremely high sensitivity, 
wherein sounds produced at the average 
voice amplitude can be heard as far away 
as 60 feet. Should the sensitivity be too 
great, the operator has only to reduce the 
current flow to any value below 60 milli- 
amperes and this sensitivity will drop in 
direct proportion. 

The Amplifier 

The Amplion Corporation of America has 
produced a microphone input amplifier that 
will operate in connection with this micro- 
phone. It supplies the energy necessary 
from 110-voIt 60-cycle current, eliminat- 
ing all batteries. It has one stage of audio 
amplification, bringing the energy level of 
this microphone up to a value equal to a 
phonograph pickup. This amplifier has 
three controls. One control regulates the 
voltage so that it can be adjusted to the 
current value regardless of the fluctuations 
on the 110-volt supply. The second con- 
trol regulates the amount of current that 
is to be put through the microphone, mak- 
ing it possible for the operator to adjust 
the microphone for any degree of sensi- 
tivity. The third control regulates the 
volume of the energy put out by the ampli- 
fier so that any adjustment of volume can 
be realized regardless of the sensitivity 
adjustment. This amplifier has a very 
unique circuit, which was necessary to 
obtain such flexibility. This circuit does 
not employ any of the conventional meth- 
ods of grid biasing, making it possible to 
obtain a special patent on this new unique 
circuit. Due to the high voltage and the 
high resistance characteristic of this micro- 
phone, it is possible to locate said micro- 
phone as far as 1000 feet away from the 
microphone input amplifier without suffer- 
ing any material loss in either quality or 

The Horn 

The Amplion type M-10 Horn is a 10-foot 
exponential air-column horn, designed to 
operate in connection with the Amplion 
Giant Dynamic Horn Unit. This horn has 
a remarkable flat performance curve from 
60 cycles to 6000. It is exceedingly light, 
weighing only 48 pounds, in view of its 
large size and sturdy construction. It is 
made of a wood fiber specially treated with 
a special type of paint which is neces- 
sary for protection against inclement 
weather and for the efficient projection of 
all audio frequencies. 

The Units 

The Giant Dynamic Unit which is used 
in connection with this horn is a remark- 
able invention. Its distinct and unique 
features lie in the fact that a double sound 
chamber is employed so that both the low. 
and the high frequencies are taken off the 
same diaphragm. This makes possible a 
much wider frequency range than ever be- 
fore realized on a speaker unit. The result 
in its performance is that a remarkable 
tonal separation is immediately noticed. 


A new type of Reco dimmer has been 
developed by the Reynolds Electric Com- 
pany, Chicago. The company states that 
no longer is it necessary for a skilled oper- 
ator to be in constant attendance, for the 
new type dimmer flasher affords perfect 
automatic control, and is capable of produc- 
ing the stage's most difficult mobile color 

This dimmer is also for use in producing 
dimming and color-blending effects in the 
theatre interior, fountains, etc. It grad- 
ually dims lights in 50 steps from bright to 
dark and back to bright. There is no limit 
to the number of colors that may be softly 
dimmed and dissolved into one another. 


A new rectifier for motion picture pro- 
jectors has been placed on the market by 
the Garver Electric Company of Union 
City, Ind., manufacturers of National Mazda 

It is claimed that the new rectifier will 
produce from alternating current, up to 30 
amperes direct current of special adapta- 
bility to low intensity arc lamps. The 
rectifier, which is registered as the Garver 
Kurrent Changer, is said to feature beauty 
in design, quietness in operation, and aur- 


Harry Fischbeck, contract cameraman at 
the Paramount studios in Hollywood, has 
developed a new lens for closeups and por- 
traits and according to reports this new 
lens gives a third dimension effect. 

As a tryout, this new lens is being used 
for all the closeups of Clara Bow and her 
supporting cast in "The Saturday Night 
Kid." Fischbeck claims that he is now 
working toward the perfection of his new 
lens where it will permit depth photog- 
raphy and medium and long distances. 


A new material for treatment of acous- 
tical faults and preparation of desirable 
acoustical conditions, has been developed, 
being called Halezite. Use may be made of 
it in the construction of theatres, of studio 
stages and sets, and of furniture. It is a 
synthetic lumber, made out of cornstalks, 
chaff, wood shavings and other waste ma- 

Working in a New York laboratory, two 
men have developed a chemical binder 
which, when sprayed over shredded corn- 
stalks, woodchips and the like, and sub- 
jected to tremendous pressure, produces in 
fifteen minutes a synthetic lumber board in 
any shape or size desired. 

Fine veneers, as well as colored wall- 
board especially desirable for theatres and 
studios, are an important development of 
the process. It is said to be cheaper than 
natural wood. Its sound-proof qualities 
and fire-resisting qualities are more than 
ten times those of wood, and it has a high 
electrical resistance, thus making an excel- 
lent insulator. 

The New York Testing Laboratories, re- 
ported in part : 

"The composition was found to saw, 
plane and file easily without splitting or 
excessive tearing. The material has about 
the same holding power when nailed as the 
better class of wood, with no tendency to 
split. The density and hardness of Halezite 
composition fall within the range from that 
of soft to hard natural woods. It possesses 
tensile strength considerably in excess of 
pine or equal to red oak when taken across 
the grain. The water absorption tests 
show no disintegration whatsoever. In the 
boiling water tests, while the commercial 
ply wood joints all opened, there was no 
separation of Halezite veneer from the core, 
nor any blistering of the top plies on Hale- 
zite board. Nor was the cornstalk board 
affected to any extent by the continuous 

"In the fire tests, the board shows more 
than 200 per cent better fire-resistant qual- 
ities than pine wood. 

"We are particularly impressed with the 
sound-proof qualities of Halezite composi- 
tion. Our tests show that the cornstalk 
lumber has about ten times the sound-proof 
value of pine lumber, an interesting factor 
to be considered for modern building con- 

Projection Engineering, September, 1929 

Page 57 




MANY times, a suggestion 
from the outside — an un- 
biased opinion — saves needless 
loss of time and money. 

The complete resources, the 
combined experience of the en- 
gineers of the Perryman labora- 
tories are available to help you 
solve your vacuum tube prob- 
lems. This group developed 
and perfected the famous Pat- 
ented Perryman Bridge and 
Tension-Spring now incorpo- 
rated in Perryman Radio Tubes. 

Submit your problem in writing, 
giving complete details. Your letter 
will receive our immediate attention. 
The recommendation of our labora- 
tories will be forwarded to you 
within one week. 



Laboratories falB and Plant 

Hudson Boulevard, North Bergen, N. J. 

The Tube 
with the 


Acme Wire Products 

Parvolt Filter and By-Pass Condensers 
Coils — Magnet Wire Wound 

Varnished Insulations 
Magnet Wire — All Insulations 

All products made to Recognized Com- 
mercial Standards, including those of: 
National Electric Mfrs. Assn. 
Radio Manufacturers Assn. 
American Society for Testing Materials 

For 25 years manufacturers and sup- 
pliers to the largest and most discrim- 
inating users. 

The Acme Wire Co. 


Branch Offices 

New York Cleveland 

52 Vanderbilt Ave. Guardian Bldg. 


842 N. Michigan Ave. 

The Lock-Up 

Fig. 673 — "Hallowell" Steel Bench Drawer Without 

Cover — for Wooden Top Work — 

Benches and Tables 

The cut on the left shows 
the "HALLOWELL" Steel 
Bench Drawer as it looks 
when ready for business. 

Its construction is such 
that it can be placed wher- 
ever most convenient. 

Fig. 849 — "Hallowell" Steel Bench Drawer for Steel 
Topped Work-Benches and Tables 

Key: A — Runner; B — Master Keyed Lock; C — Catch for Bolt of 
Master Keyed Lock; D — Tray; E — Cover. 

A work bench without a "HALLOWELL" 
Steel Bench Drawer and a suit of clothes 
without pockets aren't just right — somehow. 

Without a Drawer the Bench is soon lit- 
tered with tools and looks a mess and the first 
thing you know tools will be missing, time 
will be wasted, jobs delayed and profits 

A "HALLOWELL" Steel Bench Drawer 
holds all of your tools, you turn the key and 
they are safe and ready at hand the moment 
you need them. 

Four standard sizes carried in stock. 

Just write for full information and 

Standard Pressed Steel Co. 


Box 533 

Branches : 


Page 58 

Projection Engineering, September, 1929 

■ ', ii ™ 


'I ECVMC 1 ¥*HOWf 

i1vg pictures 

public adores! 




ROLA loudspeakers, Ions noted for their 
quality, are now provided for every purpose 
demanding the utmost in fine sound repro- 

These electro-dynamic loudspeakers operate at 
approximately twice the sensitivity of competing 
dynamics, yet without increase of field energizing 

Kola reproducers have proven rugged and depend- 
able under the most exacting conditions. The 
Kola exclusive welded-to-housing construction, 
adjustable center pole tip, ventilated field wind- 
ings, and moisture-proof materials insure repro- 
duction of unusual reliability. 

The highly desirable compactness and simplicity 
of the Kola loudspeakers is apparent at a glance. 
A side-by-side comparison will quickly demon- 
strate their superior reproduction qualities, Kola 
provides the consistently brilliant and reliable 
performance required today by your users. 

The Rola model illustrated above Is C-90: an electro-dynamic 
unit with 9-inch diaphragm, field coil wound to 2500 ohms. 
75 to 150 volts D.C. It is especially well adapted to amplifiers 
using 245 tubes in push-pull combination — for radio receiving 
sets, electric phonographs, and auditorium Installations. 

Inquiries for details, blueprints and prices 
from responsible manufacturers are solicited. 




2570 E. Superior Ave. 45th & Hollis Sts. 


Jenkins 8C Adair Condenser Transmitter 


The type C condenser transmitter is the result of two years actual 
experience, during which these instruments have been used under all 
conceivable conditions, and in practically every part of the world where- 
broadcasting or electrical recording is carried on. In addition to their 
excellence as pickup devices, they have proven to be extremely durable 
and rugged, and have shown a minimum upkeep cost. 

The type C transmitter is built for 6 or 12 v. A battery, and 180 v. 
B battery. The filament draws % amp., and the plate, 3 to G M. A. 
The amplifier has a single stage and uses a standard tube. The trans- 
mitter unit is heavily gold plated, and the case is finished in dark 
brown enamel. 20 ft. of special double shielded cable with plug and 
socket are supplied. Our bulletin No. 6 describes this instrument in 

1500 North Dearborn Parkway, Chicago, U. S. A. 

Cable Address : 

Telephones : 
Superior 3 7 2 


E- offer to manufac- 
turers interested, in. 


tne services of a dependable organization, 
well established in tbe entire foreign field 


Manufacturers' Export Managers 

116 Broad Street, New York, N. Y. 


2-Button Type 

For Public Address, etc., list. . .$25 
Standard Broadcast Model, list . . $75 

Condenser Models for Film and Record Work, 

list $250.00, $300.00 

Also Desk and Floor Stands, Covers, Cords, etc. Miniature 

Microphone, Paper Weight, Radiator Ornament. Die Cast, 

Bronze finish; prepaid on receipt of $1.00. 

Dealers everywhere 



Fred Garner Co., Gotham Eng. & Sales Co., C. C. Langevin Co., 
9 S. Clinton St. 50 Church St. 274 Brannon St. 

Projection Engineering, September, 192!) 

Page 59 

Specialists in 




Write Our Engineering Department 


335 West Madison St., 
Chicago, 111. 



Widely Used For Reason of Their Neat 
and Efficient Construction, Dependability, 
Conservative Rating and Most Reasonable 

Our new and remarkable 
types HV, rated at 550 
rms EAC, 800 v DC, in- 
corporate a high voltage 
filter of excellent electri- 
cal characteristics. Very 
small in size, exceed- 
ingly light in weight, 
unbelievably accurate in 
rated capacity, these non- 
inductive units are solv- 
ing the problems of space 
conservation and filter 
dependability. Unex- 
celled for Power Supply 
and Power Amplifier 

Not merely keeping pace with the times, but actually setting the 
precedent time and again, Flechtheim is proud to be able to 
offer a new compact condenser unit of noteworthy achievement. 
Type HV is finding increased use by radio men everywhere. 
Made in block form, tapped 0-2-4-4 mfd with a rating of 750 
rms RAC. A Universal Filter block that will serve for any 
amplifier tubes, from the 171 to the 250s. For stationary rack 
amplifiers and for portable work, they can be relied upon to 
filter out the last vestiges of a ripple and to stand up for long 
periods of continuous operation. Its unlimited uses warrant 
your interest, for it will improve any power pack or amplifier. 
Also, another new High Tension Filter block, type TC244, 
tapped 0-2-4-4 mfd rated at 1000 v DC, 750 rms RAC Made 
up of our regular 1000 volt filter condensers. 

Send For Our New Fall Catalog 

136 Liberty St., New York City, N. Y. 


- — guaranteed f 

With our greatly increased manufacturing facilities 
at Maiden, Mass., and at Cranford, N. J., we abso- 
lutely guarantee prompt delivery of Resistors for 
EVERY Resistance Need for at least the next eight 
months, no matter how large or how small the order. 
Our factory facilities and our complete line of qual- 
ity resistances will enable us to satisfactorily take 
care of your requirements. We can give you WHAT 
you want, WHEN you want it. 


Veritas Resistors 

are supplied in either cartridge or pigtail 
type, and are made in four sizes with 2 
watt, 5 watt and 1 watt ratings. Capacities 
range from 500 ohms to 10 megohms. The 
Lynch Veritas Resistors have the metallic 
resistive coating fused to the inside of the 
glass, and can run a great heat without 
change in value. Not affected by humidity 
non-absorbent. It is as perfect a resist- 
ance as can be made. 


Dynohmic Resistors 

Furnished in cartridge or pigtail type, capa- 
cities ranging from 250 ohms to 10 meg- 
ohms, '/2, 1 and 2 watt types. The resist- 
ance element is based on the famous metal- 
lized principle which has proved its supe- 
riority where accuracy and uniformity are 
of paramount importance. 

Special sizes of ALL Lynch Resistors can be made to 
order on very short notice. 

Lynch Resistors are specially suited to the exacting needs 
of manufacturers of sound and light projection equipment 
— theatrical and home talking movies — home entertain- 
ment equipment — cameras, recording and amplifying 
devices — television, etc. 

Approved by leading engineers. 

Endorsed by test and experimental laboratories. 

Employed by scientific apparatus and 
precision instrument makers. 

Selected by discriminating radio receiver manu- 

Send us your specifications. Get our prices. Let us 
send you samples. Be prepared for any emergency 
that may confront you. Descriptive folder upon 

Lynch Manufacturing Company, Inc. 
1775 Broadway (at 57th St.,) New York, N. Y. 

(Manufacturers oj 

Quality Radio Products 

Page 60 

Projection Engineering, September, 1929 



VISITRON PHOTOELECTRIC CELLS are standard with most manufacturers of 
sound-on-film equipment. Since 1925 G-M VISITRON cells of the alkali metal hydride 
type have been used for talking Moving Pictures, Television and hundreds of investiga- 
tional projects. Specialization on the problem of developing a superior photoelectric 
cell of highest sensitivity, instantaneous response and long life has resulted in a product 
which has met with universal acceptance by leading engineers in the field of sound 

For Quality in Reproduction Specify "G-M VISITRON" 


1801 Grace Street 

Chicago, 111. 

A New Air Column Speaker Made Along 
Entirely Different Lines — Getting Away 
From Antiquated Concepts and Methods 

that's MILES 

New Heights of reproducing Power and Realism, based 
on years of intensive research and development. 

Performance that has won leading manufacturers of 
LIC ADDRESS EQUIPMENT . . . that will win 
YOU by a single trial. 

Write for our various type speakers for every occasion. 


"Builders of Acoustical reproducers since 1923" 

31 West 21st Street, New York, U.S.A. 

Telephone GRAmercy 5081. Cable Address: "Milesman"— 
N. Y. 





Fireproof brick construction. 
The coolest spot on the beach. 
Invigorating breezes from ocean on East and 
Lake Holly on West. 

Bright, airy outside rooms, parlor suites 
and apartments, private baths, superior 
cuisine — Surf bathing, riding, fishing, golf, 
dancing, private tennis court and children's 




Manufacturers, Engineers — Kindly keep Projection Engineer- 
ing informed of the NEWS of your organization. Notices of 
changes in executive and engineering personnel, removals, expan- 
sions, new products, etc., are carried each month in the various 
departments of the magazine. Be sure that Your activities are ade- 
quately reported. 

Projection Engineering, September, 1929 

Page 61 

The Burt Reproducer for Talking Motion Pictures 

Burt Reproducer on Powers Projector 


Synchronous Motor Drive (110 or 220 volts, 50 
or 60 cycles). Prevents variation in speed 
from variation in line voltage, or projection 

The Super Cells used require only two stages in 
head amplifier, hence less distortion. 

Ease of Threading. When running disk or silent, 
the Sound-on-Film unit is not threaded. Sound- 
on-Film threads as easily as through a Powers 

Turn Table Is Accessible, being up high at the 
side of the machine. 

Easy to Install. Installation can be made by 
the ordinary operator, and wire man. 

Projector Head is driven by its main drive gear 
and is not required to drive any part of the 
sound equipment. 

Only Three Shafts: (1) Motor Drive Shaft, 
(2) Sound Film Shaft, (3) Disk Table Shaft. 

Variable Si>eed can be used for making schedule 
by driving the head off the Powers Motor, when 
running silent. Change from synchronous drive 
to variable speed drive requires about ten 

No Universals — No flexible couplings, flexible 
shafts, or long unsupported shafts are used, as 
these produce tremolo. 

Fire Hazard Is Decreased by use of this equip- 
ment. Failure of take-up does not cause film 
to pile up in light. 

Write for Bulletin No. 291 

Manufactured by 



900-904 East California St., 

Pasadena, Calif. 

For Amplifiers: — Poly met high-wattage resistors 
Poly met high-voltage filter condensers. 

For Equalizer Networks: — Polymet small fixed con- 
densers — Polymet resistors. 

For Power Transformers, Audio Frequency Trans- 
formers, Impedance- Adjusting Transformers, Loud- 
speaker Units: — Polymet Coils ("Polycoils") 

Send for our catalogue giving complete specifi- 
cations of Polymet Products. 
We will gladly supply samples and work with 
you to meet particular specifications. 

Polymet Mfg. Corp. 

839-A East 1 34th St. 
New York City 

Polymet Products 






FOR YEARS the name of CROWE has 
been synonymous with fine escutcheons 
and name plates, and the demand for 
CROWE products in the radio, phono- 
graph, and electrical fields attests to this 

WE ARE prepared to submit to manu- 
facturers in the sound and light projec- 
tion industry samples and estimates on 
name plates, segments, dials, scales, spe- 
cial embossings and escutcheons. 

CROWE ENGINEERS will give careful 
personal attention to each manufacturer's 
problems, and invite consultation — with 
no obligation on your part. 

"Travel by Ait 

Use Ait Mail" 

Crowe Name Plate 8 Manufacturing company 
175 6 Grace St., Chicago, 111. 

Page 62 

Projection Engineering, September, 1929 

JANETTE Motor-Driven 
Speed Reducers 

Quiet, smooth-running machines consisting of motor 
and worm-gear reducer in one compact unit. Motor- 
end frame is cast integral 
with the gear housing, a 
unique construction conducive 
to compactness and perfect 
shaft alignments. Eeductions of 
20 to 1 to 50 to 1. Motor speeds 
1750 or 1150. Sizes 1/30 to 
1/3 H.P. 

Write for 
Bulletin SR-529 



Transforms DC 
to AC to operate 
AC radios, elec- 
tric talking ma- 
chines, public 
address systems 
and motion pic- 
ture sound equip- 
ment in DC dis- 

Janette Mfg. Company, 

Singer Bldg. 
149 Broadway 
New York 

561 W. Monroe St., 

Real Estate 
Trust Bldg. 

Speed Reducer 
specially design- 
ed for talking 
motion picture 
machines. Motor 
speed 1750 RPM; 
turntable speed 
:j3Mj RPM. 


Michrophone Mixing Panels, Power Supply Panels and Racks, 
A.C. Operated Speech Input Amplifiers, Public Address Amplifiers 
for Every Purpose. 


55 E. Wacker Drive, CHICAGO 


Two Button Microphone 
Model No. 29 

The Model 29 Ellis Microphone is of the two- 
button stretched diaphram carbon granule 
type. It renders true, natural reproduction. 
The carbon hiss which is characteristic of 
many microphones is at an exceptionally low 
level. Its response to all audible frequencies 
is uniform. This microphone has no har- 
monics of its own and will give no distor- 
tion. Withstands rough handling without 
losing its fine adjustment. 
Covered by a mechanical and electrical guar- 
antee for one full year providing the unit 
is not mishandled and also providing that a 
milliameter is used in the circuit, care being 
taken that not more than 14 milliamperes 
is allowed to pass through each button. The 
remarkable feature of this microphone is that 
sufficient sensitivity is obtainable for all prac- 
tical purposes with a consumption of only 5 
milliamperes at 3 volts. A factor of safety is 
provided in allowing 10 milliamperes to be 
used on each button without danger of burn- 
out. This great sensitivity is obtained with- 
out minimizing the carbon content or creating 
diaphram resonance. Sufficient carbon is 
used to insure durability. 

Diameter 3.4", over all thickness 1.5". Espe- 
cially recommended for all broadcast station 
use, public address work, etc. Representatives 
desired for a few open territories. 

No. 2 'IN 
Nickle Finish 

No. 29SB 

Statuary Bronze 
Finish ' 


* " LIST 


General Sales Office 
333 West Madison St., CHICAGO, ILL. 

Telephone CENtral 0292 

Television Scanning Discs 

Standard 12" Aluminum Disc with mounting for %" shaft either 24, 
48, 60 holes on spiral each, $8.00. Steel Bushing for mounting on %" 
shaft each. 75c. G-10 Neon Lamp for Synchronizing Motor speed, 75c. 
These Discs are now being used by leading Television Developing Engineers. 
Special Discs made to your specifications. Standard Neon Lamp plate 
size 1 3 ,£" x l 1 /^" stands steady load of 50 milliamperes each, $8.00. 

3541 Michigan Ave., Detroit, Mich. 

PHOTO CELLS, neon lamps, special high 
vacuum or gas filled tubes, and noise-free 
liquid grid leaks, manufactured to specifications. 

150 West 22nd St. New York City 


Acme Wire Co 57 

Ad. Auriema, Inc .• 5S 

American Transformer Co . . .Third Cover 
Amplion Corp., of America . 

Amplisound Systems, Inc 49 

Amrad Corp., The 3 

Arcgo Laboratories, Inc 62 


Best Manufacturing Co 8 

Burt Scientific Labs. Robert C 61 


Cameron Publishing Company 6 

Clarostat Mfg. Co 53 

Crowe Name Plate & Mfg. Co 61 


Daven Radio Corp 60 


Electro-Acoustic Products Co 62 

Elkon. Inc 51 

Ellis Elec. Laboratory 62 

Enterprise Optical Company 

Back Cover 

Flechtheim & Co., Inc., A. M 59 


G-M Laboratories, Inc 60 

General Amplifier Co 64 

Int'l. Resistance Co 5 


Janette Mfg. Co 62 

Jenkins & Adair, Inc 58 

Lynch Mfg. Co., Inc 59 

Miles Manufacturing Corp 60 

Perryman Elec. Co 57 

Pohl, Arthur M 62 

Polymet Mfg. Corp 61 

Projectionist Sound Institute 63 


The Rola Company 58 


Shure Brothers Co 59 

Shakeproof Lock Washer Co 64 

Standard Pressed Steel Co 57 


Universal Microphone Co 58 

Ward Leonard Elec. Co. . . .Second Cover 


Zapon Co., The 7 

Projection. Engineering, September, 1929 

Page 63 




Was Created in Response to a Pressing Demand for a Correspondence School of 
Electrical Acoustics by Those Who Are Now Identified with the Art of Talking 
and Sound Pictures — Also for the Thousands That Will Have to Be Drawn in to 
Meet the Ever-Increasing Demand for Sound Engineers. 


These courses which are prepared 
by the best authorities on Sound 
will qualify you as an Electrical 
Acoustic Engineer as well as keep 
you informed at all times of the 
many improvements that are tak- 
ing place daily in this rapidly ad- 
vancing art. Our technical depart- 
ment will help you solve your indi- 
vidual local problems at all times 
free of charge. This service has 
already saved many thousands of 
dollars to theatre owners. 


The purpose of these 
courses is to give to you 
all of the available 
knowledge of the art and 
the underlying funda- 
mental principles of 
sound in an everyday, 
plain-talk language that 
anyone is able to thor- 
oughly understand so 
that you will be capable 
of operating and servic- 
ing any make of sound 


In the 20,000 theatres throughout the 
United States and Canada, which now 
employ approximately 50,000 projection- 
ists, it is estimated that less than 5% of 
this number are qualified to fill the posi- 
tion as Sound operators. Many thousands 
of new men will have to be taken into 
this field as fast as theatres are wired for 
sound as the additions of sound doubles 
the number of operators required. This 
condition will create many thousands of 
positions at salaries ranging from $75.00 
to $200.00 per week. 

The tuition for these courses is very reasonable and is payable in easy installments as you 
study. Also you have the added convenience of studying at home in your spare time. Fill out 
and mail the below coupon today for special scholarship proposition. 


F. A. JEWELL, Gen. Mgr. 

P. O. Box No. 28 Easton, Pa. 

P. O. BOX No. 28, EASTON, PA. 


Please send me by return mail full details of your special 
Scholarship Proposition on Sound Projection. 



City State . 

Page 6$ 



is the manner in which many critics have 
expressed themselves after enjoying a sound 
demonstration with GENERAL AMPLI- 
FIERS and we believe this fittingly describes 
our devices. 

You will undoubtedly have to supply much 
sound apparatus and if your first installation 
meets with complete satisfaction you are in 
line for some interesting business. The am- 
plifier is the nucleus of all sound installations, 
so why not be safe with a GENERAL 
AMPLIFIER? We offer a laboratory-tested 
device and one guaranteed against defects 
in workmanship. All GENERAL AMPLI- 
FIERS possess unusually flat frequency char- 
acteristics and provide for the full undis- 
torted power output of the tubes employed. 

We maintain a free engineering service and 
are desirous of co-operating at all times. 
Consult us freely and write for Bulletin 
PE-1 today. 

Model GA-20 (Less Tubes) $225.00 


27 Commercial Ave. 
Cambridge, Mass. 

565 Washington Blvd. 
Chicago, 111. 

274 Brannan St. 
San Francisco, Cal. 

Projection Engineering, September, 1929 

twisted' Biting leetti 
°f Steel 

TIGHTEN the nut against the SHAKEPROOF 
Washer and it's there to stay. Gripped by 
twisted steel teeth, around the whole circum- 
ference, it can't loosen — applied pressure with 
a wrench alone can break its hold. SHAKE- 
PROOF Lock Washers were developed for one 
purpose — to lock nuts. That they do this 
superlatively well is indicated by their univer- 
sal adoption in over a hundred and fifty differ- 
ent American industries. Today SHAKEPROOF 
is the standard lock washer. It should be on 
your product. Let us send you samples to 
prove to yourself the merits of SHAKEPROOF., 

Lock Washer Company 

7* [ Division of Illinois Tool Works J ** **■ 

XS09 North Keelcr Avenue Chicago, Illinois 

V. S. Patents 1,419,564; 1,604,122; 1,697,954. 

Other Patents Pending. Foreign Patents. 



2509 Nonh Keeler Ave., Chicago, 111. 

Please send me samples of 

□ Shakeproof Lock Washers to fit bolt size__ 

□ Shakeproof Locking Terminals, size 

Firm Name 





— / 

Williams Press, Inc., new york — Albany 


Overcome This Obstacle? 

Between the amplifier and loud speaker lies the source of con- 
siderable difficulty in attaining perfect reproduction of sound and 
talking pictures. 

Our engineers, — thoroughly experienced in such a highly special- 
ized field, — have been particularly successful in eliminating this 

If YOU have yet to overcome this obstacle, consult — 




Transformer builders for more than 28 Years 
1 78 Emmet Street Newark, New Jersey 


♦THEYf ARE .♦♦*■ 



Sold only by subscription 
$2.00 per year 


-~ .-...■■■.. ^ .■■■■ ■. ■■^-.I.w — ,— — — I j j l llll ,! ... ! 

1 ^ 

New York Parks 


PAM Equipped 

In Central Park, New York, the prq : 
grams such as Goldman's Band, speeches 
originating in the shell, etc., are picked - 
up and amplified by a PAM amplifier 
similar to that illustrated at the left and 
fed over the wires to twenty-five munici- 
pal parks in other sections of the city. 

One of New 
York Parks 

2-V PAM 19 

In each of these other parks is installed 
a 2-V PAM 19, shown above, which 
supplies reproducers located at proper 
points, thus permitting simultaneous 
quality reproduction at widely sepa- 
rated points. 

The parks in your city are logical pros- 
pects for a similar type of equipment. 

Have you seen your park authorities? 

A new 16-page bulletin giving me- 
chanical and electrical characteristics, 
representative installations, and many 
new PAM amplifiers will be sent upon 
receipt of 10c in stamps to cover post- 
age. When writing ask for bulletin 
No. PE-1. 

Main Office: 
Canton, Mass. 


Factories at Canton 
and Watertown, Mass. 

Projection Engineering, October, 1929 

Page 1 



For Accurate Volume Control of Disc 
and Film Track Reproduction 

View of Vitrohm Fader 

Disassembled to Show 

Component Parts 

<2> * 

Ward Leonard Vitrohm Faders offer many features and advantages. 
Engineering details and prices will be supplied on application. 




Western Editor 

Evans E. Plummer 

Advisory Editor 
Donald McNicol 

M. L. Muhleman 

Associate Editors 

James R. Cameron 

Austin C. Lescarboura 

John F. Rider 

Vol. 1 

iNiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiu iiiiiiiiiiiiniiiiiiiiiiuiiiiiiiiiiiiiii iiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiii 

October, 1929 Number 2 


Editorial 4 

Reproducing Machine for Picture and Sound By H. PfannenstieM 15 

How and Why the Fader By Horatio W. Lamson 17 

Characteristics of Peck Amplifiers By F. A. Jewell 19 

General Report of the S. M. P. E 21 

Considerations in the Design of Audio-Frequency Apparatus By C. H. W. Nason 22 

Television Coming, But as Distinct Unit By D. E. Replogle 24 

The New Wide Film Arrives By James R. Cameron 26 

Electromagnetic Sound Pickups By George B. Crouse 27 

A Few Facts About Filters By John F. Rider 37 


News of the Industry 39 

New Developments 41 

Index of Advertisers ' 50 

Aviation Engineering 
Radio Engineering 
Projection Engineering 

Published Monthly by 

Bryan Davis Publishing Co., Inc. 

Publication Office — Lyon Block — Albany, N. Y. 

Chicago Office — 333 No. Michigan Ave., Charles Farrell, Mgr. 
Cleveland Office — 10,515 Wilbur Ave., James Munn, Mgr. 
San Francisco Office — 318 Kohl Bldg. 5 
Los Angeles Office — New Orpheum Bldg., \ Cupit and Birch 
846 So. Broadway ) 

Application for entry as second class mail matter 
at the Post Office, Albany, N. Y., pending. 

52 Vanderbilt Ave. 
New York City 

Bryan S. Davis, 


James A. Walker, 


G. C. B. Rowe, 

Advertising Manager 

Yearly subscription rate $2.00 in U. S. and 
Canada; $3.00 in foreign countries. 

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Projection Engineering, October, 1929 

Page S 

Gilby Filament Ribbon is 
recognised by leading 
manufacturers as the best 
obtainable. Look for the 
large diameter aluminum 
spool, a Gilby feature. 




Wilbur B. Driver, Pres. 
150 Riverside Avenue 





is the factor in choosing 
sound equipment. Consider 
the resistance wires that 
form the heart of the ap- 
paratus. They must perform 
under the severest tests — 
they must be dependable. 
Gilby offers a wide range 
of Resistance Wires for the 
sound engineer. Manufac- 
turers should investigate 
this precision product. We 
will be glad to co-operate 
with you in the solving of 
your wire problems. Write 
for information. 


Projection Engineering, October, 1929 





October, 1929 



OBSOLESCENCE is a weighty sub- 
ject. It contains good and bad points, 
depending where and under what 
conditions it appears. 

Obsolescence is the very foundation of the 
automotive and radio industries, and others. 
Obsolescence is the curse of many industries 
that rely on a replacement business for their 

No matter the conditions or the effects, 
obsolescence cannot be effectively curbed. 
The new is as sure as the rising sun and when 
the new arrives the old must go. 

At the moment an odd condition exists in 
the motion-picture industry. Talking and 
sound films were made possible and of com- 
mercial value through the application of prac- 
tices common to the radio and phonograph 
field. The greater percentage of engineering- 
data and new developments reach the motion- 
picture field through outside channels. So 
close and similar are the applications that 
one feels that radio and the motion pictures 
are wedded to each other. 

The difficulty may be expressed in this 
manner: the radio industry forces obsoles- 
cence in order to maintain a high sales 

level the motion-picture industry finds 

it advantageous to stave off obsolescence in 
specific cases, to prevent financial misfortune 
from befalling the motion-picture theatres. 

The theatre-owner expects his sound equip- 
ment to last over a period of many years. The 
increase in profits accruing from the installa- 
tion of sound equipment is far from being 
sufficient to cover expenditures for complete 
new equipment. Sound apparatus represents 
a large investment, particularly for the small 
theatre-owner, and unless the investment can 
be spread over a period of years financial 
ruin may be the consequence. 

Sound equipment is far from being perfect. 
Improvements are to be expected. New devel- 
opments are bound to arrive, and in short 

order, because the radio industry forces obso- 
lescence. Next year's radio receivers and 
public-address systems will be far superior 
to present models. The same holds true for 
electric phonographs. It will be recalled that 
some years ago the phonograph industry was 
forced to remodel all machines to compete 
with the greatly improved tone to be had in 
radio sets. 

Radio engineering development cannot be 
forestalled. New loudspeakers are on the 
way; improved pickups; better vacuum tubes, 
with characteristics demanding an alteration 
in audio transformers. Two amplifier circuits 
have appeared on the scene, both supposed to 
be non-infringing, that have remarkable fre- 
quency response curves. Another circuit is 
on the way that permits a single intermediate 
tube to swing a 50-watter with the greatest 
of ease. 

The developments mentioned are not only 
applicable to talking and sound pictures but 
may well become necessary. Yet, if sound 
equipment is to keep steady pace with radio, 
phonograph and public-address equipment,, 
present theatre installations may be practically 
obsolete in another year. 

It hardly seems probable that talking and 
sound picture development will be aborted; 
the industry cannot afford to arrest engineer- 
ing progress. In any event, the matter does 
not appear at all pleasant from the theatre- 
owner's point of view. 

The answer to the problem rests mainly in 
design. A large percentage of present sound 
equipment is of unit construction, thus per- 
mitting changes or additions without scrap- 
ping much of the apparatus. It would be 
well that all equipment be designed in this 
manner so that future developments can be 
incorporated without the necessity of com- 
plete revision. Flexible equipment may pre- 
vent a lot of grief. 

M. L. MUHLEMAN, Editor. 

Projection Engineering, October, 1929 

Page 5 

Page 6 

Projection Engineering, October, 1929 



Since the advent of dry metallic rectifiers Elkon has 
always led in perfection of design and record of per- 
formance. Many of the leading manufacturers have 
brought their rectifier problems to Elkon for solution. 

The signal success of Elkon rectifiers in the "A" Elim- 
inator and battery charging fields was followed by 
outstanding achievements with low voltage rectifiers 
for dynamic and other moving coil speakers. 

Again, this year, looking ahead and interpreting the 
need, Elkon introduced the new high voltage recti- 
fiers which eliminate the power transformer in 
dynamic speakers and others of moving coil type. 

Whatever may be your problem of rectification, 
Elkon engineers will be glad to co-operate with you 
in working out its solution. 

ELKON, Inc. 

Division of P. R. Atallory & Co., Inc. 



Projection Engineering, Octooer, 1929 

Page 7 




With an Introduction by S. L. ROTHAFEL (Roxy) 

fig *T*ffi 


F0,,R TH EDIT,0N „ ,„E>" T " 

1280 pages 

liSLURs 'Cfi 

500 illustrations 
Fourth Edition 

Used Throughout 

the Motion Picture 

Industry as 


Price $6.00 

Dept. of Public Instruction, 

Washington, D. C, Says: 

"There are no series of books on Motion 
Pictures in the whole library of congress as 
much used as those by Cameron. We recom- 
mend them as a complete guide to the Motion 
Picture Industry." 

Exhibitors' Trade Review: 

"The best book ever written on the subject of 

American Photography: 

"This ... is a veritable encyclopedia and the 
most complete and accurate work on the sub- 
ject. Over 1,200 pages of solid matter . . . and 
has not once failed to give satisfaction." 

Film Daily: 

"Motion Picture Projection lives up to its 
slogan the standard authority." 

Society of Motion Picture Engineers, Prog- 
ress Committee: 

"A notable publication — Motion Picture Projec- 
tion by Cameron is extremely complete, cover- 
ing all phases of motion picture engineering." 

Exhibitors' Herald and Moving Picture 

"Makes an invaluable addition to any library 
of the Motion Picture Industry. It is obvious 
that Cameron has a vast store of knowledge 
on matters pertaining to projection in all its 





With an Introduction by WILLIAM FOX (Pres. Fox Film Corp.) 
Complete information on the mak- 
ing and showing of Sound Pictures 
and Sound Picture Equipment. 


and all other systems in 
use today 

"Motion Pictures with Sound" is 
a book measuring 7% x 5 inches, 
contains 400 pages of nothing but 
"talking movie" information. It 
is bound in heavy cloth with gold 


Picture 5 

Motion Picture News: 

"In comparison with all other works on the 
market this book stands in a class by itself. 
The price is not a criterion of its worth." 

Sound Waves: 

"The best book on the subject published." 

Smithsonian Institute, Washington, D. C: 

"We greatly appreciate what you have done to 
make the subject better understood." 

Bureau of Economics, Dept. of Public In- 
struction, Washington, D. C: 

"By far the most complete manual we know of. 
The most complete work of its kind." 

American Cinematographer: 

"A book that will fill a much needed want in 
the industry. We recommend the book to all 
in any way interested in the motion picture 
business and especially those who expect to 
come in contact with any of the "Talking 
Movie' systems." 

Camera Craft: 

"Cameron has written a mighty book on a 
timely subject. It takes knowledge to turn out 
a technical book as interesting and instructive. 
The book is as minute, complete and elucidative 
as one of the best we expect from the Ger- 






Page 8 

Projection Engineering, October, 1929 

A cure for Line Voltage Ills! 

NO longer is it necessary for your 
talking picture equipment to be 
at the mercy of fluctuating line volt- 
age. You can be absolutely indepen- 
dent of all fluctuations by including 




The giant variable re- 
sistor, which, in several 
turns of the knob, pro- 
vides a wide resistance 
range. Handles 250 
watts. Available in 
14-10, 25-500, and 
200-100,000 ohm 

Provided with extra 
long nipple for mount- 
ing on slate or marble 
panel, and with special 
bracket for mounting 
on bakelite panel. Also 
ideal as variable speed 
motor control and gen- 
erator field control. 

\K7 D I r P F regarding this and other CLAROSTAT devices which, 
▼ » A^ * * *-* having set a high mark in radio, are now available for the 
peculiar requirements of picture projection and sound reproduction. 


Specialists in Radio Aids 
296 N. 6th St. -:- Brooklyn, N. Y. 

The Model Die-Casting Plant ! 



In Structure — Equipment — Methods and Personnel Allied sets a new standard 

for the industry. 

The opening of the newly constructed plant of 
the Allied Die-Casting Corporation places at the 
disposal of all users of die castings, the many ad- 
vantages possible through the combination of 
every modern facility. 

This large plant, the newest and most up-to-date 
of its kind today, is devoted to two services. . The 
more economical and more efficient production of 
finer die castings - - - and - - - the production of 
the most modern die casting machinery and its' 
installation and servicing in manufacturing plants. 

This new, model plant offers to manufacturers an 
unsurpassed organization for the manufacture of 
exceptionally delicate, intricate and involved die 
castings, in which strength, accuracy and fine finish 
are inherent qualities. 

The new Allied building has been deliberately 
planned, designed and built for just one purpose 

to permit the most economical production of 

high quality die castings, by embodying every nat- 
ural and physical advantage in its construction. 

To this model structure has been added equipment 
chosen after exhaustive tests — only. None but the 
finest has been used. The great capacity of these 
high speed tools will be utilized to the utmost in 

the hands of skilled Allied artisans, producing the 
natural result when experienced workmen use fine 

As to methods — for many years Allied has suc- 
cessfully die cast parts that had been declared im- 
possible to the art. These methods are now con- 
tinued in the new plant under ideal conditions 
that make possible even greater developments in 
the science of die casting. 

The Allied personnel is progressive. Old in die 
casting experience — but young in ability to accept 
new problems and new facts, to discard old costly 
methods and to be constantly alert to any factor 
that will make it possible to produce better die 
castings more efficiently and at lower cost. 

The entire Allied model organization, as well as 
the staff of engineers, which has been so successful 
in the solution of production and die casting prob- 
lems for some of the largest industries in the coun- 
try, is at your command for consultation at any 



Long Island City, N. Y, 

The Model Die-Casting Plant ! 

Built by 



Ettinger Security Construction Corp. 









In addition to millwright work we maintain a 
machine shop for production and develop- 
mental machine work. 




The Model Die-Casting Plant ! 


Used in the new Allied factory 

High Speed Sensitive Tap- 
ping Attachment (above) 

is simple — nothing to adjust — if 
the tap sticks or hits bottom the 
Ettco slips — the same action 
coming out. No clash of a posi- 
tive clutch — just the smooth ac- 
tion of the patented leather lined 
cone clutch. Sensitive — speedy 
— satisfactory. 

No. 1 — Tapping attachment 3/16" in steel 

Y A " in C.I $35.00 

No. 2 — Tapping attachment 5/16" in steel 

3/ s " in C.I 50 - 00 

No. 3 — Tapping attachment J A" in steel 

W in C.I 80.00 

Including Chuck and 1, 2, 3 or 4 Morse Taper Shank 

Electric Vertical Tap- 
ping Machine (above) 

110 Volt — 60 Cycle — Single 

Phase $95.00 

110 Volt or 220 Volt D.C. 

or 220 Volt A.C 100.00 



Drill Chuck 

Self tightening — Hand 


None of us have time to fiddle 
around with a key any more. 
Another thing — why stand for 
chewed-up drill shanks? 

The Ettco eliminated these 
things ten years ago. 

No. 1-A Capacity to ]/, — $5.50 

No. iy z -A " to 5/16— 6.00 

No. 2-A " to H — 6.50 

No. 3-A " to %— 9.00 

No. 3y. -A " y s to 5/ 8 _n.00 

No. 1 M.T. Shank 75 

No. 2 M.T. Shank 75 

No. 3 M.T. Shank l 00 

No. 4 M.T. Shank 1.50 

Also fitted with collars for your portable tools 
These Prices subject to Consumer's Discount of 10% 


594 Johnson Avenue, Brooklyn, N. Y. 

The Model Die-Casting Plant ! 


Are extensively used in the new Allied Factory 

Manufacturers in the New Industries are invited to 
utilize our engineering and metallurgical laboratories 
and staff in solving all problems of metal or alloy 


Communicate with us. 






528 West 30th St. 


Projection Engineering, October, 1929 

Page 13 




rot- mom i: ana theatre 

its yZ»ldr ant an ess 



The Best Theatre Pick-up, isbuilt like 
a suspension bridge. So delicately is 
it balanced, that only a feather weight 
is placed on the record . When finished 
playing a record, simply tip the head 
— it stays — no danger of ruining 

record orwoodwork. 

Perfect balance 

does it. 

The Best Theatre Pick-up is the largest, heaviest, 
* most powerful Pick-up ever designed. 

• • • 

O The Best Theatre Pick-up has by far the lightest 

ttLJtttffelW weight on the record - 

O The Best Theatre Pick-up has less needle noise. 

• • • 

/I The Best Theatre Pick-up will give by far longer 

record life. 

• • • 

C The Best Theatre Pick-up has a response curve 
which follows, almost exactly that of the pick-up 
selling for over $200. 

WHEN you examine the Best Theatre Pick-up in 
. your laboratory, when you make your own inde- 
pendent tests, both individual and comparative, you 
will know that again the designers of the BBL Speak- 
er unit have made the finest product in its field. 
Samples will be sent 
to responsible m anu- 

IBffSTT Z?Wtt H'lHIII - lllll' 


Page lit 

Projection Engineering, October, 1929 




For Every 

c fhe JTcknowledded Standard 
ot Qualify since J884- 






^>\ SEATTLE ^<T 



Projection Engineering, Octooer, 1929 

Page 15 

Reproducing Machine for Picture and Sound 

New Projector for Reproducing Sound from Disc or Film 
By H. Pfannenstiehl* 

ANEW projecting machine for 
reproducing sound from either 
discs or films has recently been 
developed by the Laboratories 
for manufacture by the Western Elec- 
tric Company and is already ex- 
tensively used in theatres. To be as 
nearly universal in its application as 
possible, the frame is designed to mount 
practically all of the commercial pro- 
jector heads in use at the present time. 
Instead of being arranged in separate 
units as has been done previously, all 
the equipment — consisting of a disc 
sound-reproducing unit, an optical 
sound-reproducing unit, a film take-up 
mechanism and a motor drive — is 
mounted on a single base, as shown 
in the accompanying photographs. 

The motor, which may be for either 
d-c. or a-c, has a double ended shaft 
connecting at one end with the disc 
drive and at the other with a main 
drive gear unit from which three 
drives — two vertical and one horizontal 
— are taken. Accurate speed control is 
obtained by a vacuum tube regulator 1 . 
For sound pictures the speed is held 
constant at 1200 r.p.m., but provision 

* Special Products Development, Bell Tele- 
phone Laboratories. 



\ a i 

11 1 


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zy : :3 ^"^ 

1 * 

t. V''- ' '■'"■" 
i "' 

■ fm 


1 ' : f*'^" " c *»»5 


!i& vm B 

*i»' : : 


Fig. 2. Part of the main drive gear 
unit is hidden by the metal guard 
but the general arrangement is evi- 

has been made so that, when pictures 
are to be shown without sound ac- 
companiments, any speed from 900 to 
1500 r.p.m. may be obtained. This per- 
mits an increase or decrease in speed 
to accommodate a definite time sched- 

Accurate synchronism between the 
picture and the film or disc record is 
essential to successful sound pictures 
and steadiness of motion of the sound 
film or disc is also required. Vibra- 
tion must be eliminated. To fulfill 
these requirements all the gears are 
made to great accuracy, and the drives 
for the disc and the sound sprocket 
have flexible couplings and mechanical 

The filter for the disc drive, shown 
in Fig. 3, consists essentially of a fly- 
wheel connected by springs to the driv- 
ing gear. To avoid surges in the filter 

system, frietional damping of the 
spring connections is necessary. This 
is supplied by wrapping each spring 
with a layer of felt which is kept in 
contact with the convolutions of the 
spring by a second and outer spring 
winding. Over the felt are strips of 
metal which prevent the outer spring 
from imbedding itself in the felt and 
interfering with the proper action of 
the inner spring. The turntable itself 
serves as a flywheel. 

The filter used with the drive for 
the sound sprocket is similar in func- 
tion but differs in having hydraulic 
rather than frietional damping. 

To prevent mechanical vibration 
from being transmitted to the disc re- 
producer, cushioning is provided be- 
tween the pivot of the reproducer arm 
and the bracket that supports it. As 
an additional precaution the entire 
turntable assembly is mounted on a 
soft rubber pad. A record clamp is 
provided also to prevent the record 
from slipping on the turntable and 
thus destroying synchronism. The 
clamp is self -locking but is readily re- 
leased by lifting a small latch. 

Of the two vertical drives, geared 
to the motor shaft in the main drive 
gear unit, the front one — shown in Fig. 
2 — is connected through two universal 
joints and a telescoping shaft to the 

Fig. 1. From the operating side of 
the new machine all the principal 
elements but the drive may be seen. 

1 Bell Laboratories Record, November, 
1928, page 101. 

Fig. 3. The mechanical filter in the 
disc drive is mounted directly be- 
neath the disc itself. 

Page 16 

Projection Engineering, October, 1929 

Fig. 4. The course of the film 
through the machine may be seen 
from this photo which shows also 
the concentrated light source and 
the lens assembly. 

projector head. A separate gear 
coupling is provided at the upper end 
for each type of head used. The other 
vertical shaft is connected by a self- 
aligning shaft to a set of gears that 
drives the sound sprocket which pulls 
the film through the sound reproducing 

The horizontal shaft is connected 
through a chain and sprocket drive to 
the film take-up mechanism. This con- 
sists of a shaft, on which the film reel 
is mounted driven through a friction- 
disc type of clutch. A hold-back 
sprocket mechanism, which serves to 
prevent any uneven pull of the film 
take-up mechanism from affecting the 
uniform velocity of the film as it passes 
the lens system, is also connected to 
this drive. It is mounted in the lower 
film reel housing, as may be seen in 
Fig. 4. 

Mounted on top of the film maga- 
zine casting is a pivoted bracket carry- 
ing the sound-film reproducing unit, to 
which is fastened the projector head. 
The same bracket also mounts the 
projector arc lamp. It is pivoted about 
the center of the sound sprocket and 
may be tilted from the horizontal to 
40° below. A jack screw is provided, 
and adjustment at any angle is ob- 
tained by means of a hand wheel. 

The sound-film reproducing unit con- 
sists of a sprocket for pulling the film 
at a uniform velocity past an aperture 
plate, an exciting lamp, a lens system, 
and a photoelectric cell. The general 
arrangement may be seen from the 



diagram of Fig. 5 and from the views 
of Figs. 4 and 6. 

Light from the concentrated filament 
source is focused by a condensing lens 
on a narrow slit as shown in Fig. 7. 
An image of this slit is then focused 
on the film by a high quality objective 
lens, and light passing through the 
sound track on the film falls on the 
photoelectric cell. 

When polarized by a proper voltage, 
the current output of the photoelectric 
cell is proportional to the light falling 
upon it. The cell circuit is inherently 
of high impedance and small energy 
output so that it is very necessary to 
guard against local electrical inter- 
ference. To accomplish this a vacuum 
tube amplifier is mounted on the ma- 
chine as closely as possible to the cell. 
The amplifier serves the double pur- 
pose of increasing the energy level and 
making the energy available across a 
low impedance circuit. The vacuum 
tubes are mounted on a spring-sus- 
pended platform to prevent vibration 
from causing noise in the output cir- 

Fig. 7. The optical system is simple 
in detail but very accurate in ad- 

Fig. 6. To avoid local electrical dis- 
turbances the amplifier is mounted 
directlv beneath the photoelectric 
cell. Their relative position is here 
plainly seen. 

Due to the addition of several fly- 
wheels and various mechanisms to the 
regular projector mechanism, a longer 
time than unual is required for the ma- 
chine to come to rest after the power 
is shut off. This is objectionable at 
times of film breakage, and to correct 
it a brake has been provided controlled 
by a foot pedal shown in Figs. 1 and 6. 
Depression of this pedal first shuts off 
the power and then applies a brake to 
the motor flywheel. The machine is 
restarted by lifting the brake pedal, 
which first releases the brake and then 
closes the motor switch. 

Many special features have been pro- 
vided in addition, such as adjustable 
legs, allowing a variation of ten inches 
in height, and a mechanism for shift- 
ing the projector a small amount in 
the horizontal plane to compensate for 


Fig. 5. Details of the sound-film 
reproducing unit are here shown. 

the difference in width of the picture 
on the silent- and sound-picture films. 
Advantage has been taken of all recent 
improvements and experience so that 
the new Western Electric reproducing 
machine embodies the latest improve- 
ments in sound-picture projectors. 


TELEVISION is something quite 
different from the usual sound 
broadcasting. Both arts may 
be based on the same broad 
radio essentials, but in practice many 
differences are encountered. For one 
thing, it is far easier to fool the radio 
ear, with just an approximation of 
music and speech, than it is to fool the 
radio eye or television broadcasting, 
with incorrect pictorial values. 

The engineers of the Jenkins Tele- 
vision Corporation in the Jersey City 
laboratories have found the practical 
problems of television far more dif- 
ficult than were at first anticipated. 
In the pick-up of images, for instance, 
the usual sound broadcasting practice 
was followed, working with the equip- 
ment in the open laboratory. However, 
the many inductive interferences 
picked up by the delicate equipment 
and exposed conductors soon convinced 
the engineers that they had to work in 
grounded copper mesh cages and with 
thoroughly shielded apparatus and con- 
ductors. Again, the finest resistance- 
coupled amplifiers employed for so- 
called distortionless amplification in 
sound and laboratory practice, were 
found inadequate for the extraordinary 
requirements of television. Special 
amplifiers had to be developed. Still 
again, the first film pickup machines, 
utilizing simple scanning discs, proved 
to have an angular movement in 
scanning the film frames, due to the arc 
traveled by the scanning holes, together 
with the steady downward movement 
of the film image itself. Therefore, 
new and improved scanning methods 
had to be developed. 

Projection, Engineering, October, 1929 

Page 17 

How and Why the Fader 

Technical Data on the Design, Characteristics and Application of 

Typical Faders 

By Horatio W . Lamson* 

WE assume that all of our 
readers are familiar with the 
effective motion-picture tech- 
nique, the fade-out, whereby 
the close of a scene is dissolved by- 
restricting the field of view towards 
the center of the picture frame, and, 
at the same time, reducing the in- 
tensity of illumination. This is usually 
accomplished in the studio by slowly 
closing one or two iris shutters while 
the camera is in operation, or the 
fade-out may be produced in the pro- 
jection booth by the manipulation of 
an iris shutter on the projector. With 
the advent of synchronous and non- 
synchronous sound accompaniment for 
motion pictures, the need arose for an 
analogous acoustical fading-out device, 
the fader. 

The purpose of this instrument 1 is 
twofold. The acoustical condition of a 
theatre, due to its dimensions, archi- 
tectural features, and especially the 



J l 

» .. — .. .. vvw 1 

1 ii ii 



Fig. 2. Circuit of the simplest form 
of fader. 

size of the audience, varies consider- 
ably from time to time, so that the 
fader serves first of all as a con- 
venient means for controlling the vol- 
ume level of the reproduced sound in 
order to achieve the most natural and 
pleasing results. The proper monitor- 
ing of a sound presentation to meet 
the existing conditions contributes 
greatly to the success of the program. 

The fader also provides for reducing 
the output of an expiring film or disc 
sound track to zero and subsequently 
building up the level of the new sound 
track to the proper value. An abrupt 
change between the sound tracks at 
full volume levels gives rise to unde- 
sirable transients in the electrical sys- 
tems. By the use of the fader the 
change from one to the other can be 
made in such small steps that it is 
not perceived by the audience, and 
transients are minimized even though 
the transfer is made as quickly as 
possible. To accomplish these pur- 

Fig. 3. Circuit arrangement used 
when a transformer is interposed 
between the pickup and the am- 

poses the fader is built in the form of 
a two-sided or bilateral attenuator. 
We propose to discuss the relative 
merits of various types of faders. 

Voltage Divider Type 

The simplest scheme is shown in 
Fig. 2, Pi and P 2 represent two pick- 
ups (for film or disc tracks), and s 
is a movable contact which slides along 
the resistances R and connects to the 
grid of an amplifier tube. Here, be- 
cause the tube draws no energy, the 
fader operates as a simple voltage 
divider having a total resistance of 
2R. The load R in which each pickup 
is terminated should have a value ap- 
proximating the impedance of the 
pickup if it is desired to match 

The adjustable resistance in all of 
these faders may be constructed in one 
of two forms : as a continuously-ad- 
justable slide-wire or as a step-by-step 
attenuator in which a contact-stud 
type of switch adjusts the attenuation 
in predetermined discrete increments 

to give any desired calibration scale, 
which, however, is usually made uni- 
form in decibels. The slide-wire type 
may likewise have a scale calibrated 
uniformly in decibels if the form upon 
which the wire is wound be cut in the 
proper shape. 

The calibration of the arrangement 
shown in Fig. 2 is simple, since no 
power is drawn from the output. If r 
be the resistance between s and the 
filament, then the number N of deci- 
bels attenuation for any particular 
scale position of s is given by 


# = 20 log—. (1) 


It is often desirable to interpose a 
transformer between the pickup and 
the amplifier. In this case the fader 
arrangement shown in Fig. 3 might 
be used. Here the values of R should 
be quite large so that the currents 
drawn from the secondary coils of the 
transformers Ti and T 2 will not be of 
sufficient magnitude to injure their 
frequency-response characteristics. The 
calibration equation is, of course, the 
same as that for the arrangement of 
Fig. 2. 

Current Attenuator 

The faders function in both Figs. 2 
and 3 purely as voltage dividers. When 
these methods are used, it is highly 
desirable that the fader be made an 
integral part of the amplifier so that 
the lead connecting s to the grid of the 
tube may be shielded and kept as 
short as possible. Such a procedure is 
feasible in non-synchronized equip- 
ment, but it is not so desirable with 

* Engineering Dept., General Radio 

1 Horatio W. Lamson, "How and Why the 
Talkies," General Radio Experimenter, III, 
December, 1928 and January, 1929, and 
Projection Engineering, Sept., 1929. 

Fig. 1. At the left is the fader proper: at the right is the "dummy" 
or auxiliary control. In practice the two are mechanically coupled. 

Page 18 

Projection Engineering, Octooer, 1929 

Fig. 7. Schematic diagram for a fader like that shown in Figs. 
1 and S. The connections for the selector switch are not shown. 

synchronized apparatus where it is 
more convenient to have the fader in 
the form of a separate unit at a dis- 
tance from the amplifier and adjacent 
to the operators standing beside the 
projection machines. This service re- 
quirement may be met by making the 
fader operate not as a voltage divider 
but as a current attenuator. 

The method of Fig. 4 suggests itself. 
This is an L-type network in which 
both the series and shunt arms are ad- 
justable in such a manner that their 
sum remains constant and equal to R. 
Such an arrangement is, however, un- 
desirable for two reasons. First, the 
matching of the pickup and load im- 
pedances in both directions is poor, 
and, second, the output circuit being 
largely inductive, the attenuation for 
a given setting of the fader is a func- 
tion of the frequency. The resulting 
suppression of the higher harmonics 
causes distortion. 

These difficulties may, of course, be 
largely overcome by employing a fader 
which consists of an adjustable H- or 
T-type network after the manner 
shown (for a T-type) in Fig 5 which 
requires three sliding contacts. To in- 
crease the attenuation the two resist- 
ances Xi are increased, and, simul- 
taneously, the resistance Yi is de- 
creased. This ideal network requires 
a complicated and expensive switching 
mechanism which represents, for talk- 
ing pictures, a greater refinement than 
is warranted in practice. 

Compensated Fader 

The first step toward obtaining an 
economical design without noticeably 
sacrificing quality is shown in the com- 
pensated fader of Fig. 6 in which a 
compensating resistance C is adjusted 
in synchronism with R. This gives us 
an adjustable T-type network in which 
the total resistance of one series arm 

plus the shunt arm r remains constant. 
If the adjustable series or compensat- 
ing arm C be located, as shown, on the 
side toward the pickup, it is possible 
by proper design to maintain the im- 
pedance into which the pickup works 
at a constant value. This is the most 
important matching requirement. The 
impedance looking back from the load 
will vary between R and some mini- 
mum value, but this is relatively un- 

Fig. 4. Circuit of an L-type network. 

Fig. 5. Circuit diagram of an ad- 
justable T-type fader network. 

important. To increase the attenua- 
tion the sliding contacts are moved so 
as to reduce r and increase G. The 
calibration of such a fader presents 
too lengthy a problem for analysis 

It has been found in practice that 
the fader shown in Fig. 6 may be 
further simplified and still give suffi- 
ciently correct impedance relations to 
prevent introducing noticeable distor- 
tion. This is accomplished by giving G 
a fixed value of the proper amount. 
We now have a T-type network in 
which one series arm C is held con- 
stant, while the other series arm and 
the shunt arm are varied in such a 
manner that their sum remains con- 
stant and equal to R. This network 
gives the correct impedance looking out 
from the pickup at only one setting 
which in practice is chosen at approxi- 
mately two-thirds of the full volume 

The schematic diagram for a fader 
arranged for economy of resistance 
units and having fixed compensation 
and a step-by-step adjustment of 
attenuation is shown in Fig. 7. 

Selector Switch 

Faders for synchronized equipment 
frequently carry a selector switch (not 
shown in Fig. 7) for shifting the 
pickup terminals from the film to the 
disc sound track. Such faders are 

usually provided with fifteen steps on 
each side which are calibrated to give 
about three decibels attenuation each. 
They may, of course, be designed to 
have any desired impedance and atten- 
uation, but, in order to minimize in- 
ductive interference in these circuits 
which are connected to the input of a 
powerful amplifier 3 the impedance 
should be kept as low as possible. 
Thus, the very high impedance photo- 
electric cell is connected to an amplifier 
located adjacent to the cell. The signal 
from this amplifier, which has a low 
internal output impedance, is subse- 
quently fed into the fader at approxi- 
mately the same energy level obtained 
directly from the disc pickup. 

Use of "Pads" 

In order to minimize impedance 
variations or to match unlike input 
and output circuit impedances, it is 
occasionally the practice to install 
fixed networks or pads before and 
after the fader. Such pads neces- 
sarily introduce a certain amount of 
attenuation which must be compen- 
sated for by an increase in the over- 
all gain of the amplifying system. 

For convenience of the operators the 
fader is usually installed near one 
projector; and a dummy control unit, 
carrying a duplicate scale, is mounted 
beside the other, the dummy and the 
fader being joined by appropriate 
shafting. In certain installations aux- 
iliary change-over switching mecha- 
nisms are placed in the dummy control 

In designing the various mechanical 
features of the fader, it should be 
borne in mind that motion picture 
theatres are scattered far and wide 
over the land and that a large majority 
of them do not have immediate ac- 
cess to a trained technician. Unlike a 
vacuum tube or a photoelectric cell, 
a defective fader cannot be replaced 
or repaired in a moment's time. A 
failure of this device would seriously 
interrupt a program schedule. 

It is, therefore, of paramount im- 
portance that, in conjunction with 
the amplifiers and associated equip-' 
ment, the fader be rugged in construc- 
tion and as free from service troubles 
as good design, workmanship, and ma- 
terials can insure. The containing 
cabinet and switching mechanism 
should be ruggedly built and rigidly 
mounted so that they will withstand 
an indefinite amount of ordinary 

2 Op. cit. 

Fig. 6. Circuit of a simple type 
compensated fader. 

Projection Engineering, October, 1929 

Page 19 

Mechanical Coupling 

If a dummy control be used, there 
must be no appreciable backlash be- 
tween the dials of the dummy and mas- 
ter units. Early types of faders made 
use of a rack and pinion drive between 
the units. This was soon found to 
be unsatisfactory and was superseded 
by bevel gears and shafting equipped 
with universal ' joints to relieve in- 
accuracies in the mounting alignment. 
A recent design, introduced, and illus- 
trated in Figs. 1 and 8, eliminates the 
need for bevel gears and requires only 
straight shafting and universal joints 
between the dials of the master fader 
and the dummy control. 

Fig. S. Another view of the fader 
shown in Fig. 1, showing connec- 
tion panel and selector switch for 
changing from film to disc track. 

It has been found that a properly 
designed step-by-step contact switch is 
quieter and more reliable in its elec- 
trical operation than the ordinary form 
of continuously-variable slide wire. 

Care must be taken, however, in the 
proper choice of materials for the con- 
tact studs and brushes in order to ob- 
tain a combination which shall be free 
from oxidation which might introduce 
erratic contact resistances. Minute 
current variations produced thereby, 
after enormous amplification, would 
introduce, especially at high volume 
levels, a disagreeable scratchin'r noise 
in the loudspeakers whenever the fader 
was manipulated or subjected to 

Characteristics of Peck Amplifiers 

Technical Data on Transformer-, Resistance- and Impedance-Coupled, 
Photoelectric Cell Amplifiers 

By F. A. Jewell* 

THERE seems to be an endless 
debate over the merits of 
sound-on-film and sound-on- 
disc, as to which is the best. 
Both have their advantages as well 
as their, disadvantages, and to give 
a resume of both systems would 
wind you up just about where 
you started. But this much can be 
said in favor of sound-on-film ; since it 
is the youngest of the two, naturally 
it has not reached the state of per- 
fection that sound-on-disc has. 

It can be said that sound-on-disc has 
just about reached as high a state of 
perfection as possible and when there 
has been applied to sound-on-film as 
much engineering ingenuity as there 
has been on the former, it stands to 
reason that this system will be by far 
the most acceptable, unless its 
progress is retarded for commercial 

One of the big drawbacks to sound- 
on-film is that the electrical energy 
output of the photoelectric cell is so 
weak that additional amplification is 
required to bring it up to the same 
level of the electrical pickup. This 
additional amplifier is the big bug-a- 
boo of the system, as the greatest care 
must be used in its construction to 
overcome such things as microphonic 
noises, audio feedback or oscillation 
and the picking up of strays. 

However, due to good engineering, 
most of these problems have been 
overcome and the peck or head ampli- 
fier will deliver to the main amplifier, 
a fair duplicate of the input sound 
wave, free from most of the micro- 
phonic noises, oscillations and strays. 
Although there is room for consid- 
erable improvement in this amplifier, 
it does not present any great prob- 
lems, and if a true sound wave is de- 
livered to its input from the output of 

* General Manager, Projectionist Sound 

the photoelectric cell, this system of 
sound reproduction, even in its present 
state of development, will be far su- 
perior to the sound-on-disc method. 

Peck Amplifier Coupling 

But right here is the "nigger in the 
wood pile," so to speak — the method of 
coupling that is used to deliver the 
output of the photoelectric cell to the 
grid of the first tube in the peck 
amplifier. The method of converting 
the sound waves on the film into light 
waves, that are impinged on the photo- 
electric cell, may be perfect as well as 
the peck amplifier and the rest of the 
amplifying system, but the quality of 
reproduction in sound from the loud- 
speakers will be no better than what 
this coupling is capable of trans- 

In the author's estimation, this 
should be termed "the heart of the 
entire system," and due to its apparent 
insignificance, there has not been as 
much engineering applied to it as it 

There are two generally accepted 
methods of coupling which are used 
between the output of the photoelectric 
cell and the peck amplifier, i.e., trans- 
former coupling, as shown in Fig. 1 
and resistance coupling, as shown in 
Fig. 2. Both of these methods have 
their advantages as well as their dis- 
advantages, which will be cited here; 
and then another method will be de- 
scribed which has proven by test to 
be the superior of the two, as it over- 
comes most of the disadvantages of 
both these systems. 

Transformer Coupling 

The first thing to take into consid- 
eration in describing the circuit of 
transformer coupling, as shown in 
Fig. 1, is that the impedance of the 
photoelectric cell is in the vicinity of 
a million ohms. This involves the 

problem of designing a transformer 
with a primary impedance of a tre- 
mendously high value. When you de- 
sign a transformer of this type that 
will have sufficient reactance to repro- 
duce with true fidelity the lower or 
base notes, the distributed capacity of 
the windings, as shown by dotted lines 
in Fig. 1, will have a very low cut-off 
on the higher frequencies, short-circuit- 
ing these high frequencies to the 
ground ; so you have your choice of 
cutting off the higher frequencies in 
favor of the low or the favoring of 
the low to the high, as it is almost 
physically impossible to design a 
transformer with a straight-line char- 
acteristic curve, from 60 to 5,000 
cycles, at the impedance of approxi- 
mately a million ohms. 

However, this system is not without 
merits. Its chief advantage is the 
high ratio step-down of the trans- 
former which lowers the impedance of 
the output, which is generally located 
near the photoelectric cell and trans- 
ferring its energy through a low im- 
pedance circuit to the peck amplifier, 
which is generally located from two to 
three feet from the head of the ma- 
chine. This low impedance circuit 
from the photoelectric cell to the peck 

Circuit diagram of a transformer- 
coupled photoelectric cell amplifier. 

Page 20 

Projection Engineering, October, 1929 




Circuit diagram of a resistance- 
coupled photoelectric cell amplifier. 

amplifier has the advantage of not 
picking up strays. Furthermore, it can 
carry to the peck amplifier the output 
of the photoelectric cell through a 
shielded cable without losing very 
much of its energy at high frequencies 
despite the capacity effect between the 
high potential lead and the shield 
which is, of course, grounded. Point 
"x," Fig. 1, indicates this low poten- 
tial lead which is passed again into a 
step-up transformer which is located 
in the peck amplifier and coupled to 
the grid circuit of the first tube. 

Resistance Coupling 

Fig. 2 shows the general method 
that is used in resistance coupling. 
General practice requires the use of 
approximately one-megohm grid leak 
in the high potential lead of the pho- 
toelectric cell. This resistance forces 
the energy through a fixed condenser 
to the grid of the first tube in the 
peck amplifier. A grid leak of from 
three- to ten megohms is shunted 
across this grid and ground-circuited 
to allow the positive charge that col- 
lects on the grid of the tube to leak off 
to the ground. 

The two serious disadvantages of 
this type of coupling are, due to the 
necessity of using a grid leak of such 
high value in the grid circuit of the 
first tube, rectification takes place 
distorting the true sound-wave output 
of the photoelectric cell and as there 
are no means employed to lower the 
impedance, the energy transfer from 
the photoelectric cell to the peck am- 
plifier is through a circuit of high 
impedance. This lead must be shielded 
to prevent picking up strays and the 
capacity effect between the high poten- 
tial lead and the shield, which is, of 
course, grounded, has a tendency to 
short-circuit the higher frequencies 
which has the effect of making the 
quality of reproduction mushy or ap- 
parently behind^ a veil. Also, most of 
the overtones and harmonics which lie 
in the high-frequency range are practi- 
cally all short-circuited by this ca- 
pacity effect which is indicated by the 
dotted lines in Fig. 2. 

The other serious disadvantage of 
this type of coupling is in the recog- 
nized fact that in film recording there 
is an over-excentuation of base, and 
as resistance coupling is well known to 
favor the lower or base frequencies, 
this gives the base of lower frequen- 

cies a decided over-excentuation, which 
may be a pleasing effect to some on 
music, but will totally ruin the effect 
of speech and voice. 

Impedance and Resistance Coupling 

Fig. 3 shows a combination of im- 
pedance and resistance coupling. This 
circuit is very similar to the straight 
resistance coupling as shown in Fig. 2, 
the only additions being a variable re- 
sistance in series with a choke coil 
that is in shunt with the grid circuit 
of the first tube of the peck amplifier. 
This variable resistance, indicated as 
R-l, and choke coil, Li have the ability 
to overcome most of the disadvantages 
of both resistance and transformer 
coupling, the reason being that as re- 
sistance R-l is of low value — not ex- 
ceeding 500,000 ohms — it will not 
cause rectification of the audio fre- 
quencies that are transferred to it 
from the output of the photoelectric 

This resistance also has a tendency 
to block the high frequencies before 
they reach the choke coil which would 
normally be short-circuited by the dis- 
tributed capacity of the winding. This 

Circuit diagram of a combination 
resistance-impedance coupled pho- 
toelectric cell amplifier. 

choke coil, which is of approximately 
50 henrys value, will suppress practi- 
cally all the higher frequencies and 
with the addition of the extra resist- 
ance of R-l, will suppress the lower 
frequencies, and inasmuch as the re- 
sistance is in series between the choke 
and the grid, the distributed capacity 
of the choke becomes negligible. 

Another very decided advantage of 
this circuit is that if more base is de- 
sired for music, more resistance can be 
cut in, by increasing the value of R-l. 
Then when faithful reprodiiction of 
speech and voice is required, the value 
of this resistance can be lowered, 
eliminating the over-excentuation of 

base, making the voice clear and sharp 
with all the "s's" clearly defined. Gen- 
eral practice indicates that for music, 
the best value is approximately 250,000 
ohms ; for speech and voice, from 
50,000 to 100,000 ohms. 

Frequency Characteristic Curves 

The chart of Fig. 4 indicates the 
theoretical energy transfer from the 
photoelectric cell to the peck ampli- 
fier using the circuit of Fig. 3. Curve 
No. 1 indicates the resistance of R-l 
set at approximately 100,000 ohms. It 
will be noted that there is a decided 
cutoff beginning at approximately 
1,000 cycles and dropping to zero just 
below the 500-cycle point. Then as the 
distributed capacity of the windings 
of the choke begins to come into play, 
at approximately 4,000 cycles, another 
cutoff takes place. Inasmuch as the 
frequencies of voice and speech lie 
within this band, this value of setting 
is the most acceptable, as the hiss of 
the photoelectric cell, which lies 
within a high-frequency range above 
4,000, is practically short-circuited and 
objectionable base noises are also 
eliminated, due to the cutoff at ap- 
proximately 500 cycles. 

Curve No. 2 indicates resistance 
value of R-l at about 250,000 ohms. 
This shows that most of the base is 
included and that as the distributed 
capacity of the choke now becomes 
negligible, this allows the reproduc- 
tion of the overtones and harmonics 
of high-pitched instruments, which 
naturally gives a very pleasing effect 
for music. 

Curve No. 3 indicates the energy 
transferred with the variable resist- 
ance completely cut out which shows 
that the band of audio frequencies 
have been narrowed considerably. 

Analyzing these three curves, we 
find that if all the resistance is cut 
out, leaving only the a-c. reactance of 
the choke coil, which is of 50 henrys 
value, the resistance at 1,000 cycles is 
only 300,000 ohms, or about one-third 
of the impedance of the photoelectric 
cell. At 100 cycles, the resistance 
would be cut to 30,000 ohms and natur- 
ally this condition would short-circuit 
practically all of the lower or base 
notes, making it useless for faithful 
reproduction of both music and voice. 

At about 3500 cycles the distrib- 
uted capacity of the windings of the 
choke begins to take effect by short- 
circuiting the high frequencies to the 
ground. As all of the overtones and 

Theoretical re- 
sponse curves 
obtai na ble 
through the use 
of the coupling 
a r r a ngement 
shown in Fig. 3. 



)0 OHN/ 



— Jt— 








00 OHN 








500 1000 1500 2000 2500 3000 3500 4000 4500 5000 

Projection Engineering, October, 1929 

Page 21 

harmonics of both voice and music lie 
in the high-frequency range, as well as 
some of the fundamental frequencies, 
these are lost also. This condition is 
indicated by curve No. 3. 

For the reproduction of voice and 
speech, which are within the band of 
500 to 4,000 cycles, we find that by 
adding 100,000 ohms resistance to the 
reactance of the choke coil, this curve 
will be broadened as indicated by 
curve No. 1 of Fig. 4 which will in- 
clude this band of frequencies, and at 
the same time eliminate the back- 
ground of base which has a tendency 
to make the voice d rummy ; also as 
some of the distributed capacity of the 
winding is still taking effect, most of 
the photoelectric cell hiss will be 

For the faithful reproduction of 
music, the value of the resistance is 
increased to 250,000 ohms which will 
broaden the curve still more as indi- 
cated by curve No. 2. This seems to 
be of about the right value for the 
best reproduction of music for the 
average recording. 

Manual Pitch Control 

However, as all recordings are not 
of the same pitch, some being high 
pitched and others low, the value of 
this resistance can be adjusted to suit 
the individual requirement. This is a 
valuable asset and most of the com- 
mercial sound installations have in 
the main amplifier some method of 
controlling the pitch, but if the dam- 
age has been done at its source before 
it ever gets to the main amplifier, 
there cannot be much done about it. 

This variable resistor can be con- 
veniently located on the peck amplifier 
with different markings etched on it 
to show the resistance values, and in- 
stant changes can be made by the 
operator in changing from speech to 
music with little or no trouble. 

Reducing Capacity Effect of Shield 

"With the combination of impedance 
and resistance coupling, as shown in 
the circuit of Fig. 3, the same condi- 
tions exist as in the straight resist- 
ance coupling, shown in Fig. 2, i.e., 
the capacity between the high poten- 
tial lead and the shield. Most of this 

capacity effect can be eliminated by 
placing the peck amplifier as close to 
the head of the projector as possible 
without actually being attached to it. 
It has been proven that it is bad prac- 
tice to actually fasten the peck ampli- 
fier to the projector as the vibrating 
of the latter will set up microphonic 
noises in the amplifier which are prac- 
tically impossible to eliminate. 

This high potential lead should be 
separated from other leads that run 
to the head of the projector and placed 
in a separate shield. A piece of 
copper tubing of about one-half inch 
in diameter makes an ideal shield for 
this lead. As the wire does not have 
to be any larger than No. 30 B & S 
gauge, the spacing between the wire 
and the shield is great enough to make 
the capacity practically negligible. 

After the wire is placed in the 
tubing, the tubing should be filled 
with some kind of insulating com- 
pound to eliminate vibration. 

The circuit combining resistance 
and impedance has now been in use 
in a number of theatres for several 
months and has proven its merits. 

General Report of the S. M. P. E. 

Extracts From a Report of the Activities of the Society of Motion 
Picture Engineers by L. C. Porter, the President 

DURING the past six months 
our Committee Chairmen have 
worked hard and faithfully. 
They have initiated and are 
carrying out some interesting things. 
The Studio Lighting Committee, for 
example, reports as follows : 

"The Committee on Studio Light- 
ing has so far been able to do only 
fundamental planning for what we 
hope will eventually result in some- 
thing like a manual which will be 
of very practical value to the light- 
ing departments of the various 

"The first step along this line will 
be a bibliography of articles which 
have appeared in the Society's 
Transactions and also in other 
magazines, such as the Transactions 
of the Illuminating Engineering 
Society, on studio lighting and the 
characteristics of light sources. 
From this either entire articles or 
abstracts of the essential particu- 
lars in each article will be put 
together, so that they may be readily 
accessible and useful." 
The Journal Committee reports that 
they unanimously favor the publica- 
tion of a technical journal in place of 
our present Transactions. They are 
busy securing detail data on costs, and 
ways and means of doing this. 

The Publicity Committee puts in a 
plea for the publication of more 
S.M.P.E. material in the trade papers, 
more support from the theatre owning 

*From The S. M. P. E. Bulletin. 

interests, and more co-operation from 
the Society's members in general. 

The Standards and Nomenclature 
Committee has some new propositions 
to consider for standardization. They 
also recommend changing our present 
method of adopting standards by vote 
at our conventions to vote by letter 
ballot, after propositions are pre- 
sented and discussed at the conven- 
tions, and published in our Transac- 

The work of the Membership Com- 
mittee speaks for itself. The fact that 
we now have well over 600 members 
is mute evidence of hard, efficient 
plugging. In connection with the work 
of this committee, the Board has given 
most careful consideration to the ad- 
visability of extended foreign expan- 
sion. This seems to be closely tied 
up with the question of the publication 
of a journal. After about two hours 
discussion of the matter at the last 
Board meeting, the following resolu- 
tion was passed : 

"The Membership Committee be 
instructed to temporarily curtail 
activity in all foreign countries until 
such time as the question of the 
publication of a journal is definitely 

The Board of Governors in a strenu- 
ous 12-hour session on July 26th, con- 
sidered the above reports at length. 
Other matters of minor importance 
which the Board has discussed are : 
(1) The advisability of presenting an 
annual medal for meritorious 
work in the motion picture field. 

(2) Changes in our present letter- 

(3) Definition of "Foreign residence." 

(4) Revision of Qualifications for As- 
sociate Membership. 

(5) Honorary Memberships. 

(6) Distribution of "Aims and Ac- 
complishments" booklet. 

(7) Possibility of holding a conven- 
tion in London. 

Our Pacific Coast Section continues 
active and is proposing a series of 
joint meetings with various other mo- 
tion picture organizations. This is 
fine! The S.M.P.E., its Sections and 
members, should be co-operators. 

The London Section is growing 
steadily and holding almost monthly 
meetings which, from the reports re- 
ceived, are quite successful. 

It is to be hoped that each of these 
Sections will be well represented at 
future conventions, and that they will 
contribute freely to the Society's 

It is my firm conviction that we 
have grown to the point where it be- 
comes urgent that we have a per- 
manent office, and at least one full time 
paid officer to conduct much of the 
Society's business. The burden is be- 
coming too great to be carried in ad- 
dition to a man's regular business, 
even though divided among as many 
men as practical. To meet these 
changing conditions will require quite 
some changes in the Society's conduct, 
particularly in its finance. We are 
facing a turning point, as it were, in 
our history. 

Page 22 

Projection Engineering, October, 1929 

Considerations in the Design of Audio- 
Frequency Apparatus 

Output and High-Ratio Transformers 
By C. H. W. Nason 


THE logical trend in radio de- 
velopment is always toward 
the ideal in theoretically dis- 
associated units. The design 
of an audio-frequency amplifier, save 
for specific services where narrow fre-_ 
quency bands are to be employed, is 
therefore undertaken with the view 
that the input and load circuits with 
their attendant apparatus fulfill the 
requirements of the ideal. 

For accurate reproduction of speech 
and music, an amplifier should have a 
response essentially flat from to 15,- 
000 cycles or higher. 1 Practical limita- 
tions render this impossible, however, 
and a response from 50 to 7,000 cycles 
may be taken as ideal with present 
needs in mind. 

If this ideal is to be obtained, it is 
essential that the "reproduction fac- 
tor" or "per cent turn ratio" of the 
individual transformer be not less 
than 95 per cent as this deviation from 
the normal is magnified with the num- 
ber of stages employed with the num- 
ber acting as a geometrical factor. 
That is; if we have a reproduction 
factor of 80 per cent in each stage for 
a given frequency, when amplified 
through five stages of like character, 
the reproduction factor for that fre- 
quency will be .80 6 = .328, or 32.8 
per cent. Thus a factor of distortion 
quite tolerable in the single stage will 
be impossible of use in a multi-stage 

Besides this distortion of the fre- 
quency characteristic, there is also a 
"harmonic distortion" due to the load- 
ing of the core which will be taken up 
under the problem of "core material" 
in the second article of this series. 

The purpose of this article is to 
present the necessary data on the de- 
sign of audio-frequency apparatus in a 
theoretical treatment, to be followed 
by a series of practical design prob- 
lems in which the design of several 
representative transformers, together 
with the considerations to be employed 
in the design of the complete amplifier, 

1 See Fletcher — "Speech and Hearing"- 
D. Van Nostrand Co. 

Representative load circuits with low-ratio transformers. 

will be undertaken. To this end con- 
siderable data on available core ma- 
terials and standard core laminations 
has been collected and put into a form 
suitable for design reference. 

There are two major types of trans- 
formers classified according to design 
methods. High-ratio transformers, 
where the capacitance of the secondary 
circuit and the leakage inductances are 
of a considerable magnitude ; and low- 
ratio transformers, where the load in 
the secondary circuit may be of ap- 
preciable nature and may vary with 
frequency, but where the primary in- 
ductance and the turns ratio are the 
main factors in design. 

In designing a transformer with a 
pre-determined response curve, the 
equations for "per cent turn ratio" re- 
solve themselves into two distinct 
series. The equations employed at the 
low frequencies (from the lowest de- 
sired frequency up to about one-third 
of the range from the low-frequency 
end to the high-frequency resonant 
point) are along a separate line of 
attack from those involved in the cal- 
culations over the high frequency 

Output Transformers 

The low-ratio transformers may be 
considered to include "tube-to-load," 
"tube-to-line," "line-to-line" and other 
types involving a secondary to primary 
ratio not much greater than 1 :1, where 
the capacitance and leakage resonance 
are not consequent. 


R 2 : 

9— ^/WWWVW- 
| R3 




FIG. 3 


Fig. 3. Redrawn 
primary circuit 
and Fig. 4, an 
equivalent cir- 

At a low frequency ( Fig. 1 ) 
Ei = R t i 2 + w Li it 
But R is small as compared with w Li 
and may be neglected, ("j" is the vec- 
tor operator denoting the fact that "i" 
lags ninety degrees behind the im- 
pressed voltage. This is an imaginary 
quantity with an arithmetic value V-l, 
and must be cleared according to 
standard algebraic practice before any 
numeric value may be assigned to the 
solution of an equation, w denotes the 
"angular velocity" and has a value of 
2 t f . The eddy current and hysteresis 
losses of the core material have not 
been delineated in the figure and will 
be neglected. For all practical pur- 
poses we may write : 

If "A" is the turns ratio of the trans- 

E 2 = A Ei 
and the current in the secondary cir- 
cuit is 

i 2 = — — u. 

The primary circuit may be redrawn 
as in Fig. 3 and the transferred load 

resistance takes the form R 2 = 


The ratio Ei/E will be equivalent to 
the relationship between Zi (the im- 
pedance of Li and R 2 paralleled) and 
Zo (the impedance of the entire circuit 
looking from E). The relation 

E 2 


= A is constant and the 

value of the "reproduction factor" will 
be dependent upon 

Ei Zi 

e = ~z7 

In order to obtain the "per cent turn 
ratio" at a low frequency, it is neces- 
sary to calculate Zi/Z at that fre- 
quency and at some mid-range fre- 

Projection Engineering, Octooer, 1929 


Representative circuits with trans- 
formers functioning at high fre- 

quency where «Li has become so great 
as to be inconsequent when considered 
in parallel with R. Thus: 

x = Zi/Zo at the low frequency, 
y = Zi/Zo at 1,000 cycles 

. = (R 2 j^Li)/(R 2 + i" L,) 
X (R p + R 2 j«.'L,)/(R, + j«Li) 


x ' — 1 + [R P (R» + j«Li) /R» J«Li] 
R 2 

and y = pip 

±lp ■+- Xt2 

As was stated Zi/Zo = x/y so 


1 + R P R2 
(R p + E») i <■> Li 

(J-3 + L 5 = L 6 ) 

e C2 

FIG. 10 

Representative resonant circuit. 

Clearing the "j" term (rationalizing) 

Zi/Zo = 

'1 + 

R p E 2 

"Li (Rp + E2) 

We might more simply consider the 
equivalent circuit to be as in Fig. 4 
with R 3 representing Rp in parallel 
with the transferred load resistance. 

Rp R2 

R3 — 


Rp -)- R 2 

Zl/Zo= _ii^ 


Rs + j^L, l.+ R? 

j w Li 


and it may be seen that the primary 
inductance (Li) is the controlling fac- 

tor in determining the "per cent turn 
ratio" at the low frequencies. 

At the high frequencies the problem 
is of a different nature. The leakage 
inductance of a transformer is a func- 
tion of the coupling of the two wind- 
ings and is a result of magnetic lines 
which fail to link the two windings. 
At low frequencies its effect is of neg- 
ligible character, but at the higher 
frequencies it becomes a controlling 
factor in the design. The coefficient of 
leakage (V) bears the following rela- 
tion to (K), the coefficient of coupling 

K= M 

V Li X U 

V = 1 — K 2 
and L 3 and Lu in Fig. 5 are numer- 

L 3 = Li V 

L, = L, V 
In Fig. 6 the load characteristics have 
been referred back to the primary in 
the relationship 2 . 


A 2 

L s = 

R = 

A 2 

As shown before, <*>Li is negligible as 
paralleled with the transferred load 
at the higher frequencies and the 
equivalent circuit may be shown as in 
Fig. 7. 

Also, as before, we will proceed with 
B»/E as the criterion for perfect re- 

At a chosen high frequency 

E2/E = Rp+R 2 2 +j.Le =X 
And at a mid-range frequency where 
«L 8 is negligible in comparison 

E,/E = „ R2 „ =y 

R p + R 2 


1 + 

x/y = 

j » Le 

Rp -+- R 2 


O) Lc 

R P +R : 



and Ej/E x 100 is the "per cent turn 
ratio" as before. 

Note that L s is the factor upon 
which the characteristic curve de- 
pends at the higher frequencies and 
that it must be kept low if the high- 
frequency response is to be main- 
tained. In a given design the leakage 
inductance may always be reduced by 
decreasing the primary inductance with 
an attendant loss in the reproduction 
of the low frequencies. The problem 
to be taken up, in the second article 
of this series involves the mechanical 
design methods attendant upon re- 

2 See K. S. Johnson, "Transmission 
Circuits in Telephonic Communication." 
D. Van Nostrand Co. 

dueing L while keeping Li at its 
necessary value. 

In order to obtain the maximum 
efficiency, an impedance match (R p = 
R 2 ) is essential for the rule Rp/Rj = 
A 2 holds good and must be kept in mind 
in the design. 

High-Ratio Transformers 

The essential difference between the 
transformers already considered and 
the high-ratio transformers ("line-to- 
tube," "tube-to-tube," etc.), lies in the 
attendant loads and in the fact that in 
a high-ratio transformer the dis- 
tributed capacitances and load capacit- 
ances are far from negligible at the 
high frequencies, and in working out of 
comparatively low impedances the 
primary loading (R t ) may be of con- 
siderable moment. 

In Figs. 8 and 9 are the equivalent 
circuits comparable with Figs. 5 and 
6 previously considered. 

(I_3+L 5 = L 6 ) 


The equivalent of Fig. 6. 

The secondary load has been re- 
ferred to the primary in the sense 
R 2 = R;/A 2 and the input impedance, 
except at the very low frequencies, 
will be 

„ R 2 Rt 

R 2 + Rt 
(wLi being so high as to be inconsider- 


L4/A 2 

C 2 = CVA 2 
Ci consists of the distributed capacit- 
ance of the transformer itself in par- 
allel with the tube capacitance which 
will be 

c = c (g -f)+c (g -p)[i +s f|V a ] 


FIG. 8 


L 3 L 5 





L < 



Z | 





FIG. 9 

Equivalent circuits comparable to 
those of Figs. 5 and 6. 


Projection Engineering, October, 1929 


FIG. ^1 

° 100 


a. yu 


3 10 



H uu 

2250 uj B G 

W ||||g~ 



a 40 


(nnontii-^ p 











Two frequency 
istic curves of 
high quality in- 
terstage audio 


(This is much smaller for a thermionic 
voltmeter than for an actual amplifier 
tube and false results must be guarded 
against in making experimental runs. 
A test setup has been designed for this 
purpose in which the input capacit- 
ances of the test instruments are es- 
sentially those of an amplifier tube.) 

Now at the high frequencies we have 
Li negligible and R p , L 6 and C 2 in 
series, forming a resonant circuit 
shown in Fig. 10. 

In Fig. 11 are shown in curves 
two audio transformers. These 



not good examples of high quality 
transformers but are actual runs taken 
with a transformer used by a promi- 
nent radio manufacturer before and 
after a redesign. This redesign in- 
volved an increase in the capacitance 
of the secondary circuit and a revision 
downward of the leakage inductance. 
For an interstage transformer at the 
high frequency end, the "per cent turn 
ratio" may be considered as 

E 2 = 1 X 100 

E V «.* C 2 (A* R P + A* R t + R 2 )2 — 
O L c C 2 — l) 2 

By inspection of the formula it will 
be seen that for constant values of 
R p , R t , and R 2 the height of the 
resonance peak will vary with the sec- 
ondary self-capacitance. This illus- 
trates a means to the end. If, how- 
ever, the self-capacitance of the wind- 
ing or the leakage inductance can be 
held low in the design, the peak will 
occur outside the useful range of the 
transformer. The height of the peak 
is also proportional to R p and to R 2 
so that sufficient damping should be 
readily available in some form to keep 
the peak low. Beyond the resonance 
point, the reactance of the circuit is 
capacitative — as an analysis of Fig. 
10 would show, and the high-frequency 
cut-off occurs at the resonance point. 

Quite naturally, the d-c. present in 
the primary winding affects the in- 
ductance of the windings, and, conse- 
quently, the over-all performance of 
the transformer. This will be taken 
up in the next part of this paper in 
line with the study of the present-day 
core materials and practical design 


Kirke, "Microphone Amplifiers/' Exp. 
W. £ W.E. Vol. 5. No. 58. 

Koehler, "Audio - Frequency Trans- 
formers." Proc. I.R.E. Vol. 16, No. 12 
S. D. LaVoie (unpublished Notes, G.E. Co.)" 

(To be continued) 

Television Coming, But as Distinct Unit 

Present Status and Future of Television Outlined 
By D. E. Replogle* 


i HAT television will require dis- 
tinct and new receivers separate 
from the radio broadcast re- 
ceiving set, is now assured from 
the progress being made in laboratory 
and other television experiments. The 
question is often asked : 

"Is the increased interest in tele- 
vision manifested among experimenters 
and broadcasters significant?" 

Undoubtedly there is an increased 
interest in television. This has been 
particularly noticeable during the last 
few weeks, and television demonstra- 
tions were a feature of the Annual 
Radio World's Fair at Madison Square 
Garden and at other radio shows. 

For several months, a television 
transmitter has been broadcasting on a 
regular schedule in New York City. 
A new station is soon to go on the air 
with increased power in Jersey City. 
From Pittsburgh, experimental tele- 
vision signals can be received regularly. 

Another station has been on the air 
on an abbreviated regular schedule 
from Washington, D. C, for some time. 
In New England, we have one station 
which has been on the air intermit- 
tently for the past year. In Chicago, 

* Chairman, Television Committee, Radio 
Manufacturers' Association, Inc. 

one station is now on the air regularly 
and another is building a very modern 
television studio and transmission ap- 
paratus with prospects of being on a 
regular schedule later in the Fall. On 


the Pacific Coast, several experimental 
stations have been operating on 
irregular schedules. 

The Federal Radio Commission has 
been flooded with requests for licenses 
to broadcast experimental television 
signals, and several such licenses have 
recently been granted, so that at least 
three more television broadcasting sta- 
tions are being planued for this com- 
ing Fall and Winter. This looks like 
a very formidable array of transmit- 
ting stations. 

However, it must be understood that 
none of these stations has yet put on 
the air signals intended to have an 
entertainment value. All transmitting 
to date is, frankly, experimental, and, 
in cases where regular schedules are 
being maintained, they are for the pur- 
pose of solving the difficulties and 
problems that must necessarily arise 
from regular sustained transmission, 
such as the charting of reception zones 
in and about the broadcasting stations, 
as well as the degree of success that 
can be expected in picking up these 
signals at a distance. 

Much data has been already secured 
along these lines and much further 
data looking toward a more complete 
solution of the difficulties is expected 

Projection Engineering, October, 192'J 


to result from the research work now 
in progress. 

Dating probably last year from the 
successful demonstration of simulta- 
neous sound and sight transmission at 
the New York Radio World's Fair, 
over wire, there has been a serious 
interest in television by a number of 
manufacturing and experimental con- 
cerns, and the very recent and wonder- 
ful demonstrations staged by the Bell 
Telephone Laboratories in New York 
City in which excellent transmission 
of pictures in natural colors was 
secured, has added to this serious 
interest. Such results, of course, can 
only be achieved with transmitting and 
receiving equipment of enormous cost. 

It should be and has been to some 
extent pointed out that these demon- 
strations are laboratory possibilities 
only at the present time, and, while 
wonderful in the results accomplished, 
still fall far short of the necessary 
commercial development before tele- 
vision can become a source of public 

Advanced Knowledge of Subject 

At the meeting of the Television 
Standardization Committee of the 
R. M. A., held in Washington last May, 
a most helpful discussion was pro- 
voked on some of the outstanding 
problems that must be solved before 
television can be considered as "com- 
mercially here." This meeting, as well 
as attempting to recommend standard 
practice that would simplify the recep- 
tion of television signals, proved to be 
a meeting ground for the leading tele- 
vision engineers and experimenters in 
the industry to exchange ideas and 
experiences on problems which were 
of mutual interest. It was noted that 
in a very healthy way various groups 
of experimenters were attacking the 
problems in different ways with the 
result that our combined knowledge of 
the art was greatly furthered by free 
and frank exchanges of experiences. 

It has been the writer's privilege 
to see several demonstrations of tele- 
vision. Some have been good and some 
have been passable and others, frankly, 
have been impossible, and in all sys- 
tems there have been still unsolved 
a number of things which will event- 
ually be essential to the successful 
entrance of television as an entertain- 
ment in the home. 

While the above is a true statement 
of facts, it is not a pessimistic outlook 
on the future of television because 
never before has there been such an 
intense concentration of engineering 
talent on the subject as has recently 
been noted. The very fact that the 
problems have been analyzed and 
definitely put in form is a real ad- 
vance, and, while it is impossible to 
predict how fast progress can be made 
in solving these problems, one would 
be very lacking in faith in modern 
engineering ability if he could not 
become enthusiastic over the ultimate 
success of this new art. The element 
of time is the only thing that cannot 
be definitely estimated. 

It may be questioned whether the 
public would be interested in tele- 
vision. On this score, the literally 
thousands of letters received from ex- 
perimenters by companies who are 
known to be active in this field, seems 
to be sure proof of very healthy ex- 
perimental interest at least, and, if 
the early growth of radio is kept in 
mind, it will be remembered that it 
was just the same sort of experimental 
interest that preceded the tremendous 
popular demand for radio. 

One does not need to be a prophet 
or son of a prophet to predict the same 
sort of growth for television. In all 
probability, the immediate future will 
see decided activity among experi- 
menters in setting up apparatus to 
receive these television signals which 


I The Industry Advances | 

| ~r T was learned at the 8. M. I 
1 I P. E. Convention, in To- I 
j / ronto, that Hollyioood Stu- 
dios are producing only 5 | 
| per cent silent pictures — it is 
I estimated, as of January 30th. j 
| that nine thousand theatres are | 
| equipped with sound installa- § 
| tions — nearly six thousand pro- I 
| jectors have been exported to j 
| seventy countries throughout the 1 
I world — film exports for the first § 
1 six months of 1929 exceed by ten j 
j million feet the figures for the j 
I same period last year — labora- j 
I tories process one and one-half I 
I billion feet of film annually and | 
| — the icorld's weekly movie thea- | 
| tre attendance is placed at 250 I 
| million. = 
| (From a paper delivered by J. I. | 
1 Crabtree, at the Convention) i 

will constantly be increasing in in- 
terest, quantity and quality during the 
coming year. 

Talking Picture Films 

Analysis of the present trend in 
television indicates very clearly that 
the first means of obtaining subject 
matter will be through the use of the 
talking picture films. One of the chief 
reasons for this is that the subject 
matter on films can easily be made of 
interest, can be readily handled and 
permits simplicity in the transmitter. 
Then, too, sound can be taken directly 
from the track on the film so that 
sound and sight can be easily trans- 
mitted simultaneously. 

Of course, separate channels on the 
air must be utilized for the sight and 

The next step will probably be the 
photographing of outdoor scenes, and 
by means of a quick developing film 
transmitter, put them very shortly on 
the air. " Several methods of doing this 
are now in process of completion and 
give good promise of success. 

Following this, the next step seems 
logically to be the broadcasting of 

events as they occur directly through 
a suitably designed transmitter. This, 
however, seems to be much more dis- 
tant than either of the other two 
methods of securing subject matter. 
Paralleled with the progress outlined 
will be the broadcasting from television 
studios, where the sound and sight 
of the artists will be transmitted 

To transmit and receive television 
signals, with any degree of satisfac- 
tion, it is necessary to design very 
special and costly apparatus. Whereas 
broadcasting amplifiers with a fre- 
quency range of 50 to 5,000 cycles have 
been adequate for sound transmission, 
it will be necessary to have amplifiers 
with a range of 20 to 50,000 cycles per 
second for sight transmission. This 
alone presents a real difficulty. 

This makes obvious, however, the 
fact that present radio receivers, even 
if television broadcasting were per- 
mitted in the sound broadcast band, 
would not be adequate or at all suit- 
able for half-tone reception. 

Then, too, for economic and technical 
reasons, it has been found best to 
place television broadcasting between 
the wavelengths of 100 and 150 meters 
to which none of the commercial re- 
ceivers now on the market will ade- 
quately tune. 

Because of these major reasons and 
several others that occur to the engi- 
neer, a television receiver must be a 
very different receiver in electrical 
design from that now being used for 
sound broadcast. The one conclusion 
that can be drawn from this is that 
television will require distinct and new 
receivers for its reception and that a 
so-called television attachment is 
meaningless and of no use. 

Means of Synchronization 

Synchronism or the means of main- 
taining the receiver in electrical step 
with the transmitter has, from the 
first, presented a very serious problem. 
Several methods have been tried, and, 
under certain conditions, are very 
satisfactory, but there is no simple 
method which would be satisfactory 
under all conditions yet universally 
agreed upon. The result is that the 
first television receivers that will be 
offered the public, either in kit or 
complete form, will probably make use 
of the constant frequency of the elec- 
tric light current over wide metro- 
politan areas to keep the receiver and 
transmitter in electrical synchronism. 

As the quality of television trans- 
mission and reception increases syn- 
chronism by the power house frequency 
will, undoubtedly, become less and less 
satisfactory, and there are plans under 
way now to provide a universal fre- 
quency standard on the air, to which 
transmitters and receivers alike can be 
tuned in order to hold them in exact 
electrical step. There is no certainty 
that this method will be entirely satis- 
factory, but, at present, it seems to be 
the most logical means of securing 
the proper results. 

Page 26 

Projection Engineering, October, 1929 

The New Wide Film Arrives 

Lack of Standardization on Film, Width a Menace to 
the Industry 

By James R. Cameron, Associate Editor 

WE were among those invited 
to the premiere showing of 
the new Fox Grandeur Pic- 
tures at the Gaiety Theatre 
on Broadway recently, and here wish 
to go on record with the statement that 
William Fox has another winner in 
Grandeur Pictures to keep its stable 
companion, Movietone, company. 

We have had one or two showings of 
the wide film on Broadway prior to 
the performance at the Gaiety Theatre, 
but this was the first time a full pro- 
gram made up of wide film subjects 
was offered the theatre-going public. 
The pictures were projected onto a 
convex screen that measured 35 by 17% 
feet, the width of the proscenium arch 
at the Gaiety, and we understand that 
the screen being built for use with 
Grandeur Pictures in the Roxy Theatre 
will fill that stage opening. 

William Fox is using a film just 
twice the width of the motion picture 
film used as standard today. An an- 
nouncement sent out by the Fox Cor- 
poration says : "The development of 
the Grandeur system has been an in- 
evitable result of the revolution which 
Fox Movietone brought to the motion 
picture business. The new type of 
motion picture entertainment which 
came with sound demanded equal im- 
provement in visual reproduction; 
Grandeur Pictures do for vision what 
Fox Movietone does for sound." 

New Lense Employed 

The principle of Grandeur Pictures is 
not that of magnification. The Gran- 
deur camera is equipped with a new 
type of lens which records an image of 
much greater scope in width and depth 
than has ever before been achieved, 
using film 70 millimeters wide. The 
resultant print of a finished Grandeur 
Picture, likewise twice the present 
width, is handled on specially con- 
structed projectors and requires a 
screen of unprecedented width. When 
projected onto such a screen the pic- 
tures reveal not only greater scope but 
produce steroscopic effect. 

The first offering of Grandeur Pic- 
tures was a number of shots of 
Niagara Falls. This made one of the 
finest scenic pictures ever projected 
onto a screen ; the photography was 
excellent, and the wide screen allowed 
a panorama view of the falls and the 
rapids that were inspiring. A Fox 
Grandeur Movietone Newsreel and a 
special edition of the Fox Movietone 
Follies completed a two and a half hour 

Standardization of Film Width 

The advent of the new wide film, 
*vhile giving the public a new attrac- 

tion, threatens to throw the whole 
motion picture industry into a state of 
chaos, unless something is done imme- 
diately with respect to standardization 
of the film width. 

While Fox Grandeur Pictures are 
made on a film 70 millimeters wide, 
Paramount-Lasky are experimenting 
with a film that is just a little under 
60 millimeters in width. This is the 
film developed by Lorenzo Del Biccio, 
and the Spoor film used by R.C.A. is 
somewhere between these two widths. 

Fox, through Cortland Smith, has 
gone on record as stating that they do 
not intend changing the width of their 
film, and that after years of experi- 
menting they are convinced that 70 
millimeters is the best width for their 
purpose. The Fox Corporation point 
out that 70 millimeters is the width of 
all Eastman film made today before it 
is split into ribbons of 35 millimeters, 
and the adoption of 70 millimeters as 
a standard would make it possible for 
Eastman to turn out an immediate 
supply of this raw film stock without 
having to introduce new machinery or 
cutting down from the present manu- 
factured width with the resultant 
waste in film stock this would 

Paramount-Lasky claim that 70 
millimeters is too wide for their pur- 
pose and that they prefer a film 56 
millimeters wide. Evidently, R.C.A. 
do not agree with either as they have 
set a standard of their own. 

Of course, there is nothing to hinder 
these various organizations from going 
ahead and making pictures on any 
width film they deem best. But what 
about the exhibitor? He has just gotten 
over his battle for "interchangeability" 
with respect to "sound-picture equip- 
ment," and he certainly is going to balk 
against his having to install a sepa- 
rate projector for each of these widths, 
to take care of the finished products 
of each of these producers. 

While it is the purpose of Para- 
mount-Lasky to manufacture a special 
head that will fit the projectors in use 
in the theatres today, the Fox Corpo- 
ration have entered into an arrange- 
ment with the International Projector 
Corporation whereby the later corpo- 
ration — who, by the way, are builders 
of the two standard projectors in use . 
in most theatres today — are to build 
a special projector for use with 
Grandeur Pictures. 

While no price has been set on these 
new projectors, it is whispered around 
that the installation of a single pro- 
jector will run into tens of thousands 
of dollars. This will mean another 
headache for those exhibitors who have 
recently installed sound-picture equip- 

ment, and for which many of them are 
still paying. 

One rumor has it that the Inter- 
national Projector Corporation will not 
sell these projectors outright, but will 
lease them to theatres for a period of 
ten years at a monthly or yearly fee, 
the Fox Corporation cutting in on a 
share of this rental fee. Personally, 
we believe that both International and 
Fox are at present sitting on the fence 
waiting to see which way the wind 
blows before making any public an- 
nouncement as to just what they intend 
doing regarding the installation of 
these new projectors. 

It is no secret that the head made 
for use with Paramount's Magnafilm 
was not satisfactory. During the 
special showing of "You're in the Army 
Now" at the Rivoli Theatre, on Broad- 
way, last July, it was noticed that the 
screen image was very much blurred, 
most of the characters in the picture 
being unrecognizable. Various excuses 
were offered by the Paramount crowd 
after the showing — that the picture 
was rushed through the Astoria 
Studios ; that the equipment was new 
to the men in the projection room, and 
that they did not yet understand it, etc. 
Knowing the staff of projectionists that 
Harry Rubin has in the Rivoli Theatre, 
we personally discount this last state- 
ment just about 100 per cent. 

Of course, no one doubts that the 
producers will eventually get together 
on some standard width film. Most of 
these same producers were put into the 
red ink for much more than they would 
like to admit, just because they did not 
get together a year or two ago on 
sound-picture equipment matters, and 
this fact is still fresh in their minds. 
However, if it is true that Paramount- 
Lasky and the Fox Corporation already 
have several hundreds of projectors 
and projector heads in the course of 
construction, and each of these con- 
cerns is building these machines for 
a different width film, then it is a 
simple matter of reasoning to suppose 
that one or the other is going to have 
a number of useless machines on its 
hands just as soon as a standard width 
film is established. 

New Projectors Costly to 

The addition of one or more of these 
new wide film projectors is going to be 
a costly proposition for the exhibitor, 
not counting the cost of the projector 
itself, which may run from anything 
between $10,000 and $20,000. The ex- 
hibitor will in many instances have to 
have his projection room enlarged to 
take care of the space required for this 
new machine, and we understand that 
(Continued on page 38) 

Projection Engineering, October, 1929 

Page 27 

Electromagnetic Sound Pickups 

The Design and Interpretation of Pickups and the Reproducing Network, 
With a Preface on Mechanical and Electrical Reproducing Systems 

By George B. Crouse* 

IT is the purpose of this article 
to discuss broadly the subject of 
electromagnetic phonograph re- 
production from disc records, and 
more particularly the design and con- 
struction problems of the electromag- 
netic pickup device. 

The process of electromagnetic re- 
production of sound from disc records 
comprises picking the vibrations off of 
the surface of the revolving record 
with a needle or stylus, transmitting 
them to a tiny electric generator, or 
pickup, where they are converted into 
corresponding electric oscillations, am- 
plifying these oscillations in an audion 
amplifier, and reconverting the ampli- 
fied oscillations into mechanical or 
sound vibrations by means of a repro- 
ducer, or loudspeaker. 

One is struck at the outset with the 
complexity of this process and the 
apparatus required to carry it into 
practice, in contrast with the simpli- 
city of the older mechanical phono- 
graphs, in which the vibrations of the 
stylus were transmitted directly to an 
acoustical diaphragm working into a 
horn, and one may reasonably inquire 
whether sufficient advantages are 
gained with the electrical method to 
justify the added complexity and cost 
of apparatus. 

Mechanical vs. Electrical Repro- 

Except where extreme portability of 
the apparatus is the prime considera- 
tion, the answer to this question is an 
unqualified affirmative. 

In the first place, in the mechanical 
phonograph, the volume of sound ob- 
tainable is limited by the amount of 
energy which it is possible to abstract 
from the groove of the record, with- 
out undue wear. Obviously, in the 
electrical apparatus, the volume of 
sound may be made anything we wish 
by suitable amplification, without in- 
creasing record wear. 

The importance of this feature will 
be immediately apparent in such 
applications as the talking movies, 
where it would be impossible to fill 
the large auditoriums with a mechan- 
ical phonograph, but is a simple mat- 
ter with the electrical device. The 
importance of large available volume 
is not so apparent in apparatus de- 
signed to be used in the home, until 
one has had the experience of trying 
to follow the rhythm of the music 
from a mechanical instrument above 

the noise incident to six or eight danc- 
ing couples at a house party. 

Further, the control of the volume 
of sound from a mechanical phono- 
graph is still an unsolved problem. 
Two methods have been used. Either 
the horn is throttled somewhere in its 
length, in which case its acoustic 
properties are radically changed, and 
always for the worse on small 
volumes, or needles of different stiff- 
ness are used to secure differences in 
volume. This latter method also has 
the serious defect of altering the tone 
quality as well as the volume ; unf or- 

* Consulting Engineer, Hardwick-Hindle, 
Inc. and Rudiart Laboratories Inc. 

Fig. 3. A modern pickup mounted 
on a "tone arm." 

tunately, the needle forms an impor- 
tant element in the acoustic system 
starting at the surface of the record 
and terminating at the input of the 
horn and it is impossible to design 
this acoustical system to remain un- 
altered with different needles. With 
the electric phonograph, resistance po- 
tentiometers are used, which make 
possible the control of volume without 
the slightest distortion, from the 
merest whisper to the maximum capa- 
bilities of the apparatus, by the simple 
turn of a knob. 

In the matter of tone quality, the 
electric device has a tremendous ad- 
vantage, because it can correct the 
unavoidable defects in the record. 
It is impossible to cut a disc record 
with a flat response curve. That is, 
both the very high and the very low 
frequencies must be relatively reduced 
in amplitude. 

Record Limitations 

Consider the "lateral cut" record, 
the type in most general use. In this 
type, the sound is recorded in the form 
of a wavy groove, causing the needle 
point to vibrate at right angles to the 
direction of travel of the record sur- 

face. Given a diameter of record, rate 
of revolution and time of playing, it 
will be apparent that a certain total 
number of grooves will be required, 
and that in practice the required con- 
ditions will space these grooves very 
close together. Since, for a given 
energy, the amplitude of the wave in 
the groove will be larger, the lower 
the frequency of the note to be repro- 
duced, it is necessary to sacrifice base 
note amplitude to avoid cutting 
through from one groove to another. 
The limitation on the amplitude of 
the very high frequencies arise from 
a somewhat different cause. At the 
higher frequencies, the radius of 
curvature of the wave decreases, and 
finally becomes so minute that unless 
very small amplitudes are used, the 
stylus will cut away the sides of the 
groove very rapidly. It is, therefore, 
necessary to sacrifice amplitude in the 
very high register also. In the me- 
chanical phonograph it is difficult, if 
not impossible, to compensate for 
these defects in record construction, 
whereas in the electrical apparatus, it 
is a simple matter to introduce com- 
pensating variations in the response 
curve, by suitable design of the pick- 
up or amplifier. 

A further advantage of the elec- 
trical system lies in the fact that 
filters may, at the discretion of the 
designer, be introduced into the sys- 
tem, whereby the unavoidable surface 
noise of the record may be reduced 
to a considerable extent, without seri- 
ous loss in tone quality. While the 
surface noises cover a wide band of 
frequencies, the most objectionable 
portion of the scratch has a frequency 
range of somewhere between 4,000 and 
5.000 cycles. Accurate band suppress 
sion filters may be introduced to re- 
duce the response at these frequencies. 

It will thus be seen that the elec- 
tric phonograph has many and impor- 
tant advantages over the older me- 
chanical devices. As a practical 
matter, the cost to the consumer who 
has, or is acquiring, a radio receiver, 
is less than the cost of a mechanical 
phonograph, since the audio amplifier 
and reproducer of a modern receiver 
are perfectly adapted for phonograph 
amplification and reproduction, and 
the only additional elements required 
are the pickup and the turntable, both 
of which are obtainable at small cost. 

Radio and Phonograph 

When radio broadcasting first came 
into prominence, it was a common 
belief that it would completely super- 


Projection Engineering, October, 1929 

cede phonograph reproduction, but it 
is now generally realized that the two 
devices are complimentary instead of 
mutually exclusive. For the instan- 
taneous transmission of the accounts 
of games, and events of timely inter- 
est, of political debates, speeches, etc., 
the radio, of course, has the field to 
itself, but for the best reproduction 
of music of all kinds, the phonograph 
is superior and will probably remain 
so. There are several factors which 
contribute to this superiority of the 

In the first place, electrical phono- 
graph reproducing apparatus operates 
directly from the pickup into an audio 
amplifier, and the distortion intro- 
duced by the radio amplifiers and the 
detector is eliminated. In modern re- 
ceivers, which must have a high de- 
gree of selectivity because of the large 
number of powerful broadcasting sta- 
tions operating in small areas, the 
phenomenon of "sideband cutting" is 
usually present in greater or less 
degree, with resulting loss of high 
frequencies. It must also be admitted 
that in nine cases out of ten, a radio 
receiver is not properly tuned, so that 
sideband cutting will be present, even 
though the receiver is perfectly de- 
signed. The detector is also respons- 
ible for some distortion, due to the 
introduction of second and higher 

All sound reproducing means have 
an inevitable background of undesir- 
able noise. This background noise in 
radio reproduction is due to a great 
number of factors, among which are : 
detector tube noise (due to slight 
variations of grid charge), true static 
due to atmospheric discharges, noises 
due to transients in nearby electrical 
circuits, microphonic noises, carrier 
wave noises (due to slight variations 
in the carrier radiation) and many 
others. The phonograph has only one 
source of background noise, that due 
to irregularities in the surface of the 
record. As a result, only on very rare 
occasions does radio reproduction ap- 
proach the phonograph in low volume 
of noise background. 

Not only is this superfluous sound of 
the noise background objectionable in 

itself, but where it is large, or vari- 
able, it introduces a limitation in the 
reproduction which, in the case of 
music, is very serious. To explain this 
limitation, it will be necessary to di- 
gress to discuss the human ear and its 
associated mental apparatus. Hearing 
is, of all the senses, the most easily 
tired. Whether this is due to fatigue 
in the ordinary physiological sense, or 
due to boredom on the part of that 
section of the mind which is associ- 
ated with the ear, is uncertain, but 
that the fact itself is true, will be 
apparent to anyone who recollects his 
discomfort when forced to listen to 
some monotonous sound or cadence, or 
even to one of those unfortunate in- 
dividuals whose speech is unmodu- 
lated and flat. As a result of this 
characteristic of hearing, music, to be 
pleasing, must be an ever-changing, 
ever-contrasting series of sounds. 
These changes and contrasts must 
take place in every characteristic of 
sound. Not only must the pitch 
change, the tone quality change, but 
the volume must change as well. This 
last point has often been overlooked, 
even by musicians. 

The value of volume contrasts in 
adding to the beauty of music will be 
apparent to anyone who has listened 
to a dance orchestra playing for a 
dance, and the same orchestra playing 
the same selections in an auditorium 
for concert purposes. The difference 
in the beauty and interest of the 
music is amazing. The reason is that 
when playing for dancing, the lower 
limit to which the volume can be re- 
duced, is limited by the fact that the 
sound must be sufficiently loud to be 
heard above the noise background of 
the dancing, and the possible volume 
contrasts are greatly reduced 1 , where- 
as, when playing in a hall, with a 
quiet audience, the sound can be re- 
duced almost to a whisper, or may 
rise to the maximum of which the 
instruments are capable. 

The difference between an orchestra 
playing for dancing and for concert 
is an almost exact analogy to an 
orchestra playing for radio and for 
phonograph reproduction. In radio 
reproduction, the -large amount of 
background noise which must be al- 
lowed for. requires a comparatively 
constant volume level, and volume con- 
trast is almost entirely lacking. In 
the phonograph, however, the back- 
ground noise is small, practically con- 
stant and known, so that much larger 
contrasts in loudness can be obtained, 
with a resultant of greater interest 
and beauty in the reproduced music. 

Still another factor which makes for 
better reproduction from a record lies 
in the fact that more time and greater 
care can be taken in rehearsing before 
recording, than would be practical in 
most radio programs. It is well known 
that the arrangement of pieces in an 
orchestra when playing for a present 

The side elevation of the pickup 
shown in Fig. 1. 

audience is quite different from that 
required for reproduction, and the 
latter arrangement is a matter of 
experimentation in every individual 
case. Radio programs, which must be 
new every week and must be re- 
hearsed in studios which are greatly 
in demand, obviously cannot be 
brought to the state of perfection 
which is practical in the case of 
record making. It is also obvious that 
mistakes in the rendition cannot be 
corrected in radio reproduction 2 , 
whereas, this is always done in the 
case of the phonograph. 

For these reasons, for one who de- 
sides the highest quality in musical 
reproduction, it will be apparent that 
the phonograph offers many advan- 
tages over the radio. 

In the electric phonograph, the 
problems of design of the amplifier 
and loudspeaker are no different than 
in the design of the same apparatus 
for radio reproduction. In fact the 
same apparatus is used interchange- 
ably for both. Since both of these 
elements have been fully discussed in 
the current literature, we will pass 
directly to the discussion of the elec- 
tromagnetic pickup, the device which 
forms the heart of the electric phono- 

Electromagnetic Pickups 

In Figs. 1 and 2 are shown respec- 
tively a front elevation and a vertical 
section of a modern pickup head of 
usual design. A "U" shaped per- 
manent magnet of alloy steel, desig- 
nated by the numeral 1, is provided 
with the soft iron machined pole 
pieces 2 and 3, which are generally 
supported and aligned against the 
back plate 4, of non-magnetic mate- 
rial, by screws, as shown. 

The adjacent ends of the lower legs 
of the pole pieces are hollowed out to 
support the pair of tubular soft rub- 
ber bearings 5 and 6, through which 
project the shaft extensions 7 and 8 
of the soft iron armature 9. This 
armature extends upward between the 
upper legs of the pole pieces and is 
centered there between by the two 

The front elevation of a pickup 
head. The different parts are ex- 
plained In the accompanying text. 

X A condition that can be rectified some- 
what by the super-amplification of repro- 
duced music. 

2 Suggesting canned programs as a 
worthy contribution to the art of broad- 

Projection Engineering, October, 1929 

Page 29 

soft rubber blocks 10 and 11 carried 
in the adjustable metal holders 12 
and 13. 

The lower end of the armature is 
provided with a broached hole into 
which the stylus 14 is inserted and 
clamped in position by the stylus 
screw 15. 

Surrounding the armature is the 
coil of fine copper wire 16 wound in 
the bakelite form 17. The leads of 
this coil are brought out to terminals 
carried on the terminal block 18, 
which is clamped against the back 
plate by the long screw 10, and is thus 
made to serve additionally as a clamp 
for the permanent magnet. The entire 
mechanism is enclosed in an ornamen- 
tal pressed metal cover not shown in 
the figures. 

The complete pickup head is 
mounted on a 'tone arm," a common 
form of which is shown in the photo- 
graph of Fig. 3, with pickup head at- 

The usual method of connecting the 
pickup to its associated electrical cir- 
cuits is shown in diagramatic form in 
Fig. 4, in which 16 is again the coil 
in which the electrical oscillations are 
generated. Connected directly across 
the coil is the resistance 23, of suitable 
value, and provided with the hand ad- 
justable contact 24, forming a poten- 
tiometer, the output leads of which 
are connected to the primary of the 
first audio transformer 25. The bal- 
ance of the amplifier and reproducer 
circuits are standard, and need no 

When the pickup is mounted in play- 
ing position on a moving record, the 
lateral variations in the record 
groove cause the point of the stylus 
to vibrate, which in turn vibrates the 
armature. Movement of the armature 
between the poles causes a correspond- 
ing variation in the magnetic flux sup- 
plied by the permanent magnet to be 
diverted through the armature and 
therefore through the coil, thus gen- 
erating a corresponding electrical os- 
cillation, which is properly attenuated 
by the potentiometer, amplified in the 
amplifier and reproduced in the loud- 

Interpretation of Systems 

It will be seen that the pickup and 
its associated electrical apparatus 
form a coupled mechanical and electri- 
cal and electrical system, for the con- 
version, transmission and amplifica- 
tion of a band of frequencies lying in 
the acoustical range. Very satisfactory 
and easily handled methods have been 
worked out, and are familiar to all 
electrical engineers, for analyzing the 
behavior of electrical networks in the 
transmission of alternating currents 
as functions of frequency and it has 
recently been discovered that these 
same methods may be applied to the 
analysis of mechanical systems, by 
forming electrical analogs of the 
dynamical system under consideration. 
This method immediately makes avail- 
able all of the short cuts which have 

been developed in the electrical case, to 
the mechanical problem, and is an ex- 
tremely valuable analytical tool. 

The method of forming these analogs 
is as follows : 

an equivalent mass at some one point 
of the system, as for instance, the point 
where the spring joins the bar. We 
represent this mass as an equivalent 
inductance. In a similar manner, we 


Mechanical force 

Mechanical velocity 

Mechanical dissipative resistance 

Mechanical mass 

Mechanical spring compliance 

= Electric potential 
= Electric current 
= Electric resistance 
= Electric inductance 
= Capacitance 

Consider now the simple dynamical 
system, shown in Fig. 5, comprising an 
alternating mechanical force F-F, ap- 
plied to the end of a leaf spring 26, 
connected to a bar 27 pivoted about 
the axis 28 perpendicular to the plane 
of the paper. It is also assumed that 
there is some bearing friction. This 
system may be represented by the 
equivalent electrical diagram of Fig. 

















FIG. 4 

The usual method of connecting a 
pickup to its associated electrical 
circuit is indicated in this diagram. 

6, which we form by first representing 
the force F-F as a constant potential 
generator 29. A constant potential 
generator is used to represent the 
force because the value of the force 
is supposed to be constant, independent 
of any conditions of the dynamical 
system which it is driving. 

The spring 26 will, of course, be 
represented as a condenser, and the 
question as to whether this condenser 
should be connected in series with the 
rest of the load, or directly in parallel 
across the generator is determined as 
follows. In the electrical case, a 
capacitance connected across a con- 
stant potential generator would absorb 
current, but would not affect the 
voltage in the circuit beyond the con- 
denser ; whereas, if it was connected 
in series between the generator and the 
rest of the load circuit, it would absorb 
voltage, and reduce the potential avail- 
able beyond it. 

Turning now to a consideration of 
the effect of the mechanical spring 26, 
it will be at once apparent that, due 
to the flexibility of the spring, it will 
absorb motion; that is, the end of 
the spring where the force is applied 
will move through a greater amplitude 
than the other end. The force avail- 
able at the point where the spring is 
attached to the bar, however, will, 
within the limits of strength of the 
spring, be no less than the applied 
force. It is, therefore, apparent that 
we should place the equivalent ca- 
pacity directly in parallel with the 
generator, as shown at 30. 

To represent the mass of the bar 27, 
we first determine the moment of in- 
ertia of the bar about the axis 28, and 
then convert the mass of the bar into 

convert the friction effect into its 
equivalent effect at the same point. 

We must now determine whether the 
resistance and inductance should be 
represented in parallel or in series. 
Since it is apparent that the effect of 
the resistance will be to reduce the 
motion of the bar (in other words, 
limit the current) we must put the 
resistance and inductance in series. It 
is obvious that the combination will 
be in parallel across the condenser and 
generator, and we, therefore, have the 
complete analog as shown, in the 
figure, where the inductance is rep- 
resented by 31 and the resistance by 

We may now determine any charac- 
teristic of the mechanical system by 
an analysis of the equivalent system 
by the usual and well known methods. 
In a similar manner, we may form 
analogs of any dynamical system of 
almost any complexity. 

Study of Dynamical System 

We are now in position to study the 
dynamical system of the pickup shown 
in Figs. 1 and 2, by forming the 
equivalent diagram, show in Fig. 7. 
The moving system is energized at the 
point of the stylus as the record 
rotates under it. This source of 
energy is represented by the generator 
33, which in this case, is a constant 
current generator, for the reason that 
the velocity imparted to the needle 
point is fixed by the amplitude of the 
wave in the groove, and the surface 
velocity of the record, and is not 
affected by any conditions of the load, 
within the limits of the strength of 
the walls of the groove. On the other 
hand, as in a constant current genera- 
tor, the pressure applied to the point 
of the needle will be determined by 
the load conditions. 

From the previous explanations, it 
will be clear how the balance of the 
diagram is determined. 

34 represents the compliance of the 

35 represents the total mass of the 
pickup and the mass of the tone arm 
effective at the center of mass of the 
pickup head. It is this quantity which 
prevents the pickup head, as a whole, 
following the variations in the record 

36 is the equivalent of a transformer, 
and represents the fact that the dis- 
tance between the pivot axis of the 
armature and the point of the stylus 
is different from the distance between 
the pivots and the center of the active 
upper magnetic air gaps. This factor 
is required to be represented in the 

rage 30 

Projection Engineering, October, 1929 

diagram because we are interested in 
the motion of the armature at the 
center of these upper gaps. 

37 represents the compliance of the 
rubber bearings in a direction parallel 
to the normal motion of the needle 
point. These bearings are slightly 
compressible, and this results in a 
slight absorption of motion between 
the stylus point and the upper gap. 

38 represents the energy absorbing 
factor in the rubber bearings, due to 
the motion explained under 37. 

39 represents the compliance of the 
rubber bearings to normal rotary mo- 
tion. This is represented as a series 
capacitance, since it does not absorb 
motion (equivalent to current) be- 
tween the stylus point (generator) 
and the active gap. 

40 represents the energy absorbing 
factor in the rubber bearings, due to 
the motion explained under 39. 

41 represents the effective mass of 
the armature to normal motion. 

42 represents the compliance of the 
rubber blocks. 

43 represents the energy absorbing 
factor of the rubber blocks. 

44 represents a quantity which has 
no actual equivalent in electrical cir- 
cuits, but which may be regarded as a 
negative capacity. It represents the 
upsetting pull on the armature due to 
the difference in the flux values in the 
two upper gaps when the armature is 
displaced from its center position. 

45 represents the effect of the elec- 
trical circuit as reflected into the 

The behavior of the mechanical sys- 
tem may now be completely determined 
from the characteristics of the equiva- 
lent electrical system. 

28 -- - 





FIG. 5 

<-.- — 27 

,-- 26 



A simple dynamical system of the 
needle and armature of a pickup. 

The design of the mechanical system 
must be determined in relation to the 
following factors of performance. 

(1) Sensitivity of the device. 

(2) The wear which the device im- 
poses on the record at all frequencies. 

(3) The shape of the response curve, 
(generated voltage versus frequency) 
which determines the quality of the 
reproduced sound. 

Sensitivity and Record Wear 

Considering first the matter of sensi- 
tivity, as affected by the design of the 
mechanical system, and remembering 

that 33 represents a constant current 
generator, it will be apparent that all 
impedances in shunt with the genera- 
tor should be as large as possible, to 
prevent the by-passing of current 
(velocity of motion). Thus, we 
should, for high sensitivity, use as 
stiff a needle as possible, so as to keep 
the quantity 34 high, and for the same 
reason, there should be as little side 
sway in the bearings as possible, in 
order to keep impedances 37 and 38 

Similar reasoning in regard to the 
impedances in series between the gen- 
erator and the load, shows that the 
values of these elements should be 
kept low. Thus, the quantity 41, rep- 
resenting the mass of the armature 
should be made small, or, in other 
words, the armature should have a 
very low moment of inertia ; and simi- 
larly for the other quantities in series. 

The above considerations apply, of 
course, at frequencies other than a 
natural frequency. The system will 
have natural periods of vibration, and 
some of these will in practice, lie 
within the range of frequencies to be 
translated. At these frequencies, the 
output will be limited only by the 
dissipative losses. 

Record wear occurs because of pres- 
sure, corresponding to the voltage 
of the stylus point against the side of 
the groove, and this pressure, 
which the generator is required to de- 
liver, will be different at different fre- 
quencies. As in any constant current 
generator, the voltage which the gen- 
erator will be called on to deliver, will 
depend on the impedance of the load, 
the higher the impedance, the higher 
the voltage delivered. The shunt im- 
pedances will all, therefore, tend to de- 
crease the voltage, and, therefore, the 
record wear. The series impedances 
will play the decisive part, and it will 
be obvious that the total series im- 
pedance should be as small as possible. 
At the low frequencies, it will be the 
effective mass of the armature which 
will be important, whereas at high fre- 
quencies, the quantity 42, representing 
the compliance of the rubber blocks, 
will be the controlling factor. 

Summing up these observations, we 
note that in order to obtain the desir- 
able characteristics of high sensitivity 
and low wear on the sides of the 
record groove, an armature of small 
effective mass should be employed, 
centered by rubber blocks of small 

Response Curve 

The response curve is a curve plotted 
with frequency as abscissa and voltage 
generated in the electrical system by 
the pickup with constant velocity of 
the stylus point, as ordinate. A 
theoretically perfect pickup working 
into a theoretically perfect amplifier 
and reproducer, should have a response 
curve forming a straight horizontal 
line: in other words, the voltage gen- 
erated by the pickup should be the 
same at all frequencies for the same 
velocity of the needle point. In 

practice, using present amplifiers and 
reproducers, it is desirable that the 
pickup should deviate from this the- 
oretical, as pointed out in the early 
part of this article. For our present 
purposes, however, we may assume 
that the theoretical form is the de- 
sired one, and examine the equivalent 
diagram, Fig. 7 from this standpoint. 
It will be clear at once that if the 

The equivalent electrical diagram 
of Fig. 5. 

system contained no dissipation, or in 
other words, was undamped, that the 
voltage generated at different fre- 
quencies would be widely different, be- 
cause of the varying impedance of the 
system as a whole. At the points of 
natural frequency, the impedance 
would be small and the response ab- 
normally large, or the reverse, and 
the response curve would consist of a 
series of sharp peaks and deep valleys. 
In order to avoid this, damping is 
introduced by means of the soft rubber 
bearings and rubber blocks. Rubber 
has a very high internal, or molecular 
friction, which makes it most suitable 
for this purpose, although it has the 
disadvantage that its use in the sys- 
tem also introduces a reactive effect 
because of its springiness. 

Amount of Damping 

The amount of damping which will 
be required to produce a response curve 
of satisfactory shape will depend upon 
the amount of energy stored in the re- 
active elements of the system. For 
the shunt elements, the larger the 
value of impedance, the smaller the 
energy which will be absorbed. For 
instance, if the stylus were infinitely 
stiff, it would transmit to the armature 
all of the motion imparted by the 
record to its point, and thus would 
store no energy in itself. Conversely, 
the values of the series elements, such 
as the effective mass of the armature, 
the spring reactance introduced by the 
rubber blocks, etc., should be made 
low if small dissipation in the system 
is desirable. 

It is desirable that the losses in the 
system be small for two reasons. In 
the first place, large dissipation means 
reduced efficiency or lowered sensi- 
tivity. Secondly, the energy to supply 
the damping losses must be taken from 
the record, and the larger the energy 
required, the greater the record wear. 

Turning again to the equivalent 
diagram of Fig. 7, consider the 
quantity 44, representing the effect of 
the electrical system as reflected into 

Projection Engineering, October, 1929 

Page 31 

the mechanical. The significance of 
this quantity should be clearly under- 
stood. It is the load impedance in the 
mechanical system, and all of the 
mechanical energy dissipated in it is 
converted into electrical energy in the 
electrical system. Its relation to the 
other quantities in the diagram indi- 
cates that the greater its relative 
value, the greater will be the efficiency 
of the device as a converter. 

The value of this load impedance 
will be shown in the following to be 
a function of the electrical impedance 
of the circuits into which the device 
is working, of the characteristics of 
the magnetic system of the pickup, and 
of the geometry of the magnetic air- 
gaps of the device. 

Turning back to Figs. 1 and 2, the 
electric potential is generated in the 
coil 16 due to changing flux in the 
armature 9, occasioned by the motion 
of the upper end of the armature in 
the upper air gaps. 

When the armature stands in the 
mid position, no flux from the perman- 
ent magnet will flow through it, and 
for a small displacement 8 from the 
mean position, the flux <t> through 
the armature will be 

<f> = SKi 8 


where S = the magneto-motive force 
applied to the system by the permanent 
magnet. Ki is a constant of propor- 
tionality determined by the geometry 
of the air gaps as will be pointed out 
in more detail later. 

The rate of change of flux through 
the armature will be : 

d<A dS 

— = SKi — 
dt dt 


Since the voltage generated in a 
coil is proportional to the rate of 
change of flux therethrough, the 
voltage Ee generated in the coil 16 
will be: 

Ee = Ki SK 2 T — (3) 


Where K 2 is a physical constant of 
the units employed and T is the num- 
ber of turns in the coil. 

But — is the velocity of the end of 

the armature in the air gap, and in 
forming the electrical analogs, we saw 
that velocity was equivalent to current, 

we, therefore, replace — with the sym- 

bol I m , or mechanical current, and re- 
write Equation 3 as— 

Ee = Ki K 2 ST I m 

An expression connecting electrical 
current and mechanical voltage (force) 
E,„ may be derived by considering that 
electrical current flowing through the 
coil will cause a force to be exerted on 
the armature tending to displace it 
from its mid-position, and this force, 
using the symbol of the analog, will 
be given by : 

E m = K 8 K 4 ST Ie 

Where K* is a constant (depending 
on the units employed) relating the 
flux through the armature with the 
force exerted thereon in the field of 
the upper gap, and K 3 is the constant 
of proportionality between the flux 
flowing in the armature and the am- 
pere-turns of the coil determined by 
the reluctances of the circuit. 

Now, the impedance of the electrical 
system in terms of the voltage and 
current in the system is: 


Ze = 



and therefore from Equation 4 and 
Equation 5, we may write: 


Ze = Ki K 2 K 3 K 4 S 2 T 2 — (7) 

E m 

By analogy, 

E n 

= — where Z, n is 

Z m 

the mechanical impedance, or in other 
words, the quantity 45 of Fig. 7, and 
given by: 

Ki K 2 K 3 K 4 S 2 T 2 

Z m =- (8) 


Since it was previously shown that 
in practice, Z m should be made as 
large as practical, it is important to 
examine the factors of this equation in 

The quantities K 2 and K 4 are physi- 
cal constants whose numerical values 
depend upon the units chosen, and are 
not connected with the design of the 

The constant Ki may be evaluated 
from the following considerations. Ex- 
amining the magnetic system, it will 
be seen that it is a circuit in which 



3 Hi 37 

-|^-www-^000"0 ^— |" 






R1 ^>. 

R2 iJ J ^'^ \ 

1 R6 s? 

RA^Hu : 

'■ ^jJ^R5 

FIG. 8 

Equivalent circuit diagram of magnetic pickup shown in Figs. 1 and 2. 

Generalized electrical structure of 
magnetic pickup system. 

the reluctances are arranged in the 
form of the Wheatstone bridge, so 
well known in electrical circuits, as 
shown in Fig. 8. 

In this figure, the internal reluctance 
of the permanent magnet is repre- 
sented by Ri. The magneto-motive 
force is generated in this branch as 
shown at S. The two upper gaps are 
represented by reluctances Rj and R 3 , 
and the two lower gaps as R 4 and R>. 
The armature forms the bridge arm 
reluctance R>, which is permanently 
connected in fixed relation to the lower 
gap reluctances, and in variable rela- 
tion to the upper. 

Values of R 2 and R 3 depend upon 
the areas and inversely, upon the 
lengths of the upper gaps, and, there- 
fore, upon the displacement of the 
armature. Ki is, therefore, calculated 
by the usual equations for Wheatstone 
bridge circuits, as the flux flowing in 
R« for unit magnet strength when the 
armature is displaced a unit distance 
from the center. 

In a similar manner, the constant K. 
is determined as the flux flowing in 
the armature when one unit of 
magneto-motive force is generated in 
the coil with the armature in the mid- 

The structure of the device should 
be such as to make the constant Ki as 
large as possible and this is accom- 
plished by making the length of the 
air gap as short as practicable. In 
practice, a compromise must be struck 
between the gain in sensitivity due to 
reducing the air gaps, and the loss in 
sensitivity due to the necessary stif- 
fening of the rubber blocks to prevent 
instability of the armature. 

Considered alone, it would appear 
that the constant K 4 should also be 
made as large as possible by reduc- 
ing the reluctances of the air gaps, but 
this quantity is connected in a very 
complex manner with the possible 
number of turns. The coil, considered 
as the winding of a generator, has in- 
ternal impedance, and works into an 
electrical circuit having a finite im- 
pedance, and therefore for maximum 
voltage output, there must exist a best 
relation of the internal and external 
impedances. The internal impedance is 
determined not only by the number of 
turns on the coil, but also by the 
characteristics of the magnetic circuit 

Page 32 

Projection Engineering, October, 1929 

through the coil. The factors which 
increase K 4 also increase this magnetic 
effect, and therefore, the internal re- 
actance of the coil, with the result that 
with a given load impedance, the num- 
ber of turns must be decreased and an 
experimentally determined compromise 
must be struck between the two 

The greater the magneto-motive force 
available, the greater the sensitivity, 
and the size and strength of the mag- 
net are limited only by considerations 
of cost and weight, with the added 

Explanatory diagram, illustrating 
flux path in a toroidal coil. 

limitation that the material of the 
armature must not become saturated ; 
as was shown previously, the size of 
this member cannot be increased with- 
out decreasing sensitivity and increas- 
ing record wear. 

The design of the magnetic system 
will be taken up in more detail later 
on, together with the design of the 
tone arm. 

The effective life of an electro- 
magnetic pickup will be no greater 
than the life of the permanent magnet, 
which supplies the magneto-motive- 
force for its operation. It is, there- 
fore, of great importance to the 
designer to be able to predict the 
behavior of the permanent magnet, 
which it is proposed to use in any par- 
ticular design. Unfortunately, there is 
no adequate theoretical basis on which 
to base the design of a permanent mag- 
net for any given application and re- 
course must be had to purely empirical 
data, expressed if possible in conven- 
ient mathematical form. It will be at- 
tempted, in the following, to give a 
brief summary of the empirical data 
available, and the method of applying 
it to the design of a specific magnetic 

Related Electrical Quantities 

In magnetic phenomena, there are 
recognized three measurable quantities 
expressable in definite definable units, 
which are closely analogous to three 
quantities in electrical phenomena. In 
magnetism, we have a magnetic po- 
tential, or force, usually designated as 
magneto-motive-force, which corre- 
sponds to the potential or voltage in 

electricity. The amount of magnetism 
passing through a given area, known 
as flux, is equivalent to electric cur- 
rent. Further, in any magnetic circuit, 
there is a quantity which connects the 
amount of flux flowing in the circuit 
with the magneto-motive-force. This 
quantity is known as reluctance and 
corresponds with resistance in an elec- 
tric circuit. 

In an unvarying magnetic system, 
these three quantities are related by a 
law identical with Ohm's law in elec- 
tricity, that is, reluctance times flux 
equals magneto-motive-force. 

While we have so far stressed the 
analogy between magnetic and electric 
circuits, we cannot push this likeness 
too far. There is one important re- 
spect in which the two systems differ. 
In an electrical circuit, the mainte- 
nance of current by electro-motive- 
force requires the expenditure of 
energy, whereas, the maintenance of 
magnetic flux by magneto-motive-force 
in an unvarying system, does not re- 
quire energy. In other words, an elec- 
tric battery, from which current is be- 
ing drawn, will inevitably be exhausted 
sooner or later, unless the energy gen- 
erating elements within it are replen- 
ished. A source of magneto-motive- 
force, on the other hand, will pass flux 
through its associated magnetic circuit 
indefinitely, without being replenished. 
If this were not so, it would be im- 
possible to secure a permanent magnet. 

Turning now to a more detailed dis- 
cussion of the three magnetic quanti- 
ties, defined above, it is well known 
that magnetic flux flows around a con- 
ductor carrying electric current, and 
that the amount of flux, if the con- 
ductor is located in air or in a vacuum, 
is directly proportional to the amount 
of current flowing in the conductor. 
Since electric current is an easily 
measurable quantity, it is convenient 
to measure electro-motive-force in 
terms of current flowing in a wire. 
A unit of electro-motive-force is, there- 
fore, defined as the amount generated 
by one ampere of current flowing 
through a closed electric circuit com- 
prising a single turn of wire. The 
force is directed along the axis of the 

A unit of reluctance is defined as 
that of a column of air of unit length 
and area. It is a curious fact that for 




A f 

h v 

*l ,^l 

c -' MMF. 

FIG. -10 

Flux quantity plotted against mag- 

practical purposes, the reluctance of 
unit length and area of most substances 
as also unity, the only exceptions be- 
ing metallic elements — iron, nickel, and 
cobalt, and their alloys, and a few re- 
markable substances known as the 
Heussler alloys, which are of only 
scientific importance. In the case of 
the magnetic alloys, the reluctance of 
the unit cube is very much less than 

With the above two definitions in 
mind, it is apparent that the unit flux 
will be the amount of flux flowing 
through an area of one square centi- 
meter under the driving force of one 
unit of magneto-motive-force. 

Another very important quantity in 
magnetic calculations is the flux den- 
sity, which is the amount of flux flow- 
ing across a given area divided by the 

We are now in position to consider 
the actual phenomena occurring in a 
given magnetic circuit. Collider, first, 
a toroidal coil of wire as shown in Fig. 
9, having a mean radius of r centi- 
meters, and assume further, that a 
single turn has an area of A sq. cm. 
Let there be a total of T turns of wire 
in the toroid and suppose that a cur- 
rent of I amps, flows through the wire. 
Such a system will generate a closed 
ring of flux through the turns. The 
reluctance of the flux path is evidently 
2t/A and the magneto-motive-force 
will be equal to I T. The flux density 
will be equal to I T/2m\ 

In this system, it is important to 
note that flux is maintained onl,y so 
long as the current flows through the 
wire, disappears within a minute frac- 
tion of a second after the current 
ceases and reappears in the opposite 
direction when the current is reversed. 

We now introduce a soft iron core 
or ring of toroidal shape and cross sec- 
tional area A in place of the air core 
of the original experiment, and 
notice a number of changes in the re- 
sulting phenomena. In the first place, 
the amount of flux flowing in the ring 
is enormously increased. The amount 
of this increase is measured by the 
quantity u called the permeability so 
that the new reluctance will be equal 
to 2T/A, and the flux density will be 
equal to I T/2^r. The permeability 
unfortunately is not a constant for a 
given sample of iron but varies in an 
unpredictable manner with the flux 
density existing in the iron and must, 
therefore, be determined experimentally 
for any given grade of magnetic ma- 

A further' difference between the 
magnetic system of one with an iron 
core and one with an air core is that 
in the former case, when current 
ceases to flow in the surrounding coil, 
it will be found that some flux con- 
tinues to flow in the iron. In other 
words, the flow of flux through the 
iron has created within the material 
a magneto-motive-force due probably to 
some configuration of the molecules of 
the material, which continues to exist 

Projection Engineering, October, 1929 

Page 38 

after the external magneto-motive- 
force is removed. It is this phenomena 
which makes the permanent magnet 

Representative Curves 

Putting the above statements in 
graphic form, we may lay out a chart 
of rectangular coordinance as shown 
in Fig. 10, in which the abscissa rep- 
resent magneto-motive-force and the 
ordinates represent the resulting flux 
in our toroidal iron ring. If the 
original M. M. F. (magneto-motive- 
force) and resulting flux lie at the point 
a in the diagram, the remaining flux 
at zero M. M. F. will be at some point 
o, and if the M. M. F. were gradually 
reduced from its maximum value to 
zero, the flux would follow a curve as 
shown. It will be apparent that in 
order to reduce the flux to zero, it will 
be necessary to apply an M. M. F. in a 
direction opposite to the original, and 
of a value such that the curve will be 
continued to zero flux value as shown 
at c. 

It has been found by experiment that 
the shape of this curve depends upon 
the quality and character of the iron. 
For instance, steel having a moder- 
ately high carbon content properly 
tempered will retain a great deal more 
of its flux than soft iron and will re- 
quire a much higher external reverse 
M. M. F. to reduce its magnetism to 
zero. Its characteristics will be repre- 
sented more nearly by curve d in the 
diagram. It will, however, never pass 
as much flux under high magnetizing 
forces as the soft iron, because its 
permeability is much lower and con- 
sequently reluctance much higher. 

A permanent magnet in the form of 
a closed iron ring would be of no prac- 
tical value in any application since the 
flux is all confined within the ring. 
In any magnetic device, there must 
always be an air gap. We have seen 
that in the air gap, no magneto-motive- 
force can be selfsustaining, and it has 
been further shown that just as an 
electric current flowing through a re- 
sistance generates an effective counter 
electro-motive-force, so magnetic flux 
flowing through a reluctance generates 
a counter magneto-motive-force. There- 
fore, considering curve d, suppose that 
we introduce an air gap into the 
toroidal ring such that a counter M. M. 
F. of value indicated at e is generated. 
In this case, the flux in the ring will 
have a value as indicated at /, and we 
have a complete permanent magnet 
system, with an air gap in which we 
may place an armature or a coil, or 
some other device for utilizing the flux 

It has been further found that up to 
certain values of counter M. M. F. in 
any given sample of magnetic material, 
the internal M. M. F. is not destroyed 
and when the external counter force 
is removed, the flux returns to its 
original value as g in the diagram. 
Beyond a certain critical value, the 
internal M. M. F. is destroyed and the 
steel rapidly loses its magnetism. This 

critical counter M. M. F. bears a rather 
loose relation to the total M. M. F. 
required to completely remove the mag- 
netism from the sample, and, there- 
fore, the distance zero to a is a meas- 
ure of the permanence and the merit 
of a steel intended for permanent 
magnets. This quantity has been 
named the coercive force. 

Nature of Steels 

Originally permanent magnets were 
made of tempered high carbon steel. 
As the art of building electrical meters 
became more refined, the demand grew 
for a permanent magnet which should 
have greater coercive force and con- 
stancy than that obtainable from un- 
alloyed steel. It was found that cer- 
tain alloys of iron and tungsten and 
iron and chromium had these desir- 
able properties and tungsten magnet 
steel is today used almost exclusively 
in high grade electrical indicator in- 
struments for both portable and switch- 
board work, and shows no signs of 
being replaced by any of the more 
recently discovered alloys. 

Quite recently it was found that 
alloys of iron and cobalt could be made 
which gave higher coercive forces than 
tungsten alloys. The comparison of 
these two steels is indicated approxi- 
mately in Fig. 11. 

It is important in the intelligent 
application of these alloys to under- 
stand thoroughly the difference in 
their properties. For instance, tung- 
sten steel cannot be subjected to a 
greater counter M. M. F. than that 
indicated by the point i, whereas 
cobalt steel may be subjected to a 
counter M. M. F. several times as 
great as indicated by j. Put in other 
terms, for a given length of cobalt 
magnet, we may employ air gaps of 
much higher reluctance than may be 
employed in the case of tungsten. 
However, with a correctly designed air 
gap, the tungsten magnet will pass 
more flux because of its lower internal 
reluctance. It must be pointed out 
and strongly emphasized that in a 
properly designed magnet circuit, tung- 
sten magnet is just as permanent as 
the other, and will make available a 
greater quantity of flux. It must be 
further noted that if size is not a con- 
sideration, a longer tungsten magnet 
will do all and more than the cobalt 
magnet will do. 

As a result of much experimental 
data, an empirical equation has been 
obtained by means of which the per- 
manence of a given magnet may be 
predicted. Let A g equal the area of 
the air gap, and L g = the length of the 
gap. Let Ai = the area of the magnet, 
and L, = its length. Then for tung- 
sten steel : 

A g L, 

x > 70 

L g A, 

Since the dimensional quantities are 
all ratios, it does not make any dif- 
ference whether English or Metric 
lengths and areas are used. 

For cobalt steel, containing 15% of 
cobalt, the numeric on the right hand 
side of the above expression, may be 
reduced to 35. 




Comparative coercive forces of 
cobalt and tungsten steels. 

New Moving System 

Cobalt steel has come into general 
use in electromagnetic pickups be- 
cause of the large air gaps, which it 
has been previously necessary to em- 
ploy, and because the necessary size 
and weight of the tungsten magnet 
under these conditions was. pro- 
hibitive. In a more recent type of 
pickup, however, an improved form of 
moving system is employed, which 
makes possible the use of shorter air 
gaps, and consequently the tungsten 
with its higher flux density may be 
advantageously used. 

In the design of magnetic systems 
employing permanent magnets, it is 
customary to disregard the reluctances 
introduced by the soft iron pole shoes 
since these are generally small in re- 
lation to the flux in the gap. Pre- 
cautions must be taken in the design, 
however, to prevent undue leakage be- 
tween the poles of the magnet since 
such leakage provides a path whereby 
flux is uselessly shunted around the 
working gap. The effect of such leak- 
age is to increase the quantity A g , in 
the above expression for stability. 

Desirable Characteristics of a 

The purpose for which a pickup is 
designed is to faithfully convert the 
motion transmitted to the point of its 
stylus by the record into electrical 
oscillations. The relative successive 
amplitudes and frequencies of the elec- 
trical oscillation should be an exact 
reproduction of the record groove, ex- 
cept in so far as the pickup may be 
called upon to correct compromises in 
the record cutting, or to suppress sur- 
face noises or scratch. The degree to 
which the device meets these condi- 
tions is determined by the "response 
curve," showing voltage generated for 
constant velocity of the stylus point 
at all frequencies within the range of 
the instrument. This curve, in the 
writer's opinion, should have the ap- 
proximate form shown in Fig. 12. The 
enhanced response at frequencies be- 

Page 8J f 

Projection Engineering, October, 1929 


-AAAA/W^t— || ° 

-■H2.5V. -90V. 


Circuit diagram 
of a vacuum- 
tube voltmeter 
for use in mak- 
ing frequency 

low 300 cycles is for the purpose of 
correcting the diminished amplitude of 
cut at the low frequencies, and the 
diminished response at frequencies 
above 3,000 cycles is desirable to 
partially suppress the surface noises. 
In no case should the curve show 
sharp changes in curvature, deep val- 
leys or sharp peaks, as these always 
result in unpleasant "jingling" noises 
in the output. 

Granting that the device under con- 
sideration has a satisfactory response 
curve, probably the characteristic next 
in importance from the commercial 
viewpoint, is its ability to maintain a 
uniform level of performance through- 
out its life, which should be indefi- 
nitely long. This characteristic de- 
pends on the construction, quality of 
materials, and similar factors. 

The importance of sensitivity de- 
pends very largely on the degree of 
amplification which is available, but 
when the device is intended for use 
with the audio amplifiers ordinarily 
used in connection with radio re- 
ceivers, a high sensitivity is usually 
desirable and often necessary. 

A factor in pickup performance 
which has only recently been given seri- 
ous attention is the wear on the sides 
of the record groove occasioned by the 
use of the device. The wear at the 
low frequencies is due to the stiffness 
of the armature and that at the high 
frequencies is due to the mass of the 
moving system. For low record wear, 
both the stiffness and the mass should 
be as low as possible. 

Use of Constant Frequency Records 

Probably the most satisfactory 
method of determining the response 

3 1 


FIG. -12 

curve is by the use of "constant fre- 
quency records." These are disc rec- 
ords of ordinary construction, on which 
are cut bands of grooves, each band 
being cut to impart a constant fre- 


H S < 








t--- -i 

An ideal response curve of an elec- 
tromagnetic pickup. 


Curve of pickup working into a 
resistive-impedance load. 

quency and velocity to the needle 
point. These records are available 
with frequencies from 40 cycles to 
8,000 cycles in small steps. 

The pickup is mounted and played 
on these records in the normal manner, 
the voltage output being determined by 
means of a vacuum tube voltmeter. A 
very convenient and satisfactory form 
of voltmeter for this purpose is shown 
in Fig. 13. 

In this voltmeter, an — 01-A tube 
and a — 71 tube are used. The switch- 
ing arrangement provided gives the in- 
strument a range of .2 volt to 150 volts. 
In most pickup measurements, the low 
voltage range is the only one which 
need be employed. A d-c. micro-am- 
meter is connected to the terminals 
marked "output." The instrument is 
calibrated on 60 cycle a-c. against a 
standard a-c. meter of commercial de- 
sign. If care is taken to adjust the 
filament voltage to the same value 
every time the instrument is used, the 
calibration remains constant over a 
long period. 

Certain precautions must be observed 
in making these measurements. In the 
first place, if curves taken at widely 
separated intervals of time are to be 
compared, it is obvious that the cali- 
bration of the voltmeter must be 
checked and corrected at frequent in- 
tervals, and that the turntable speed 
should be checked and adjusted be- 
fore every series of tests. 

The actual velocity imparted to the 

needle point by the constant frequency 
records is not exactly the same, the 
differences being marked on the record 
in dbs. The voltmeter reading must 
be properly corrected at each fre- 
quency by the factor given. In addi- 
tion to these stated corrections, it was 
generally found that the cutting is not 
quite uniform throughout an entire 
length of groove on any one frequency, 
and if high accuracy is desired, it is a 
good plan to take the average voltage 
reading at several points on the 

Effect of Load 

An electromagnetic pickup is an 
electric generator with a relatively 
high internal impedance, and, there- 
fore, its voltage output will be a func- 
tion of the impedance of the load. 
Further, its internal impedance is 
largely inductive in character and, 
therefore, varies with the frequency 
which it is generating. For this rea- 
son, it is important that the response 
curves be run with the pickup con- 
nected to a load circuit, which is very 
close in characteristics to that with 
which it will be used. In Figs. 14 and 
15 are shown curves of the same 
pickup. In Fig. 14, the load comprised 
only the very high resistive impedance 
of the vacuum tube voltmeter shown in 
Fig. 13. In Fig. 15, the pickup was 
working into the primary of a high 
quality audio transformer having a 
3 :1 ratio secondary to primary, the 
secondary being connected in the grid 
circuit of a lighted audion. It will be 
observed that the effect of the trans- 
former load is not only to reduce the 
voltage at all frequencies, but that 
marked changes in the shape of the 
curve are also introduced by the load. 

It often happens that defects in the 
transformer are shown up in the course 
of such tests. Wherever a sharp peak 
or valley occurs in a response curve 
which cannot be easily accounted for 
from the design of the pickup, the 
transformer may be suspected. This 
can generally be checked by using the 
same transformer with a pickup of en- 
tirely different constants. If the peak 
or valley again occurs at the same fre- 
quency it is fairly positive evidence 
that the transformer has abnormally 
high or abnormally low impedance at 
this frequency, and that the trouble 
is not in the pickup. The effect of a 
transformer having an abnormally low 
impedance at a certain frequency is 







"N. ..... 




Curve of a pickup working into a 
transformer primary. 

Projection Engineering, October, 1929 

Page 35 

illustrated in the curves of Figs. 16 
and 17, which were taken with two 
pickups of radically different designs, 
and yet both curves show a deep de- 
pression at exactly 1,500 cycles. 

Effect of Tone Arm 

The tone arm also plays a very im- 
portant part in the performance of the 
pickup, and response curves should al- 
ways be run with the pickup mounted 
on the tone arm, for which it was de- 
signed. The character of the mount- 
ing affects principally the low fre- 
quencies. The effect of mounting is 
illustrated in the curves of Figs. 18 
and 19, which were made by the same 
pickup. In the curve of Fig. 18, the 
pickup was mounted on the tone arm 
supplied by the manufacturer and, as 
will be noted, very good characteristics 
were obtained. In the curve of Fig. 
19, the pickup was mounted on an arm 
which allowed the entire weight of the 
pickup to rest on the needle point. 
The result was an enormously en- 
hanced response in the low frequency 
region, but with violent changes of 
curvature, as will be seen from the 
curve. In this connection, it should 
be pointed out that a correctly de- 
signed tone arm will impose a weight 
on the needle point of not much over 
four and one-half ounces. If a greater 
pressure than this is required to ob- 
tain satisfactory response at low fre- 
quencies, the device will cause undue 
wear on the bottom of the record 

Frequency Characteristics 

As an illustration of what may be 
expected from pickups of present com- 
mercial design, the curves of Figs. 20, 
21 and 22 should be examined. Curve 
20 is regarded by the writer as being 
as close an approximation to the ideal 
curve as is commercially possible. It 
will be noted that this curve has a 
broad peak in the lower frequency 
range, and falls off rapidly in the 
range above 3,000 cycles, thereby ef- 
fectively suppressing the undesirable 
scratch noises. The curve has nowhere 
any sharp change of curvature nor any 
high peaks or deep valleys. The curve 
of Fig. 21 is at first glance much more 
uniform in response, but it will be 
noted that it has a large rise in the 
scratch frequency range and practi- 
cally no increase of response below 
100 cycles, where the records are de- 





Effect on curve of transformer with 
abnormally high or low impedance. 

ficient. Such a curve, in the writer's 
opinion, is not as desirable as that of 
Fig. 20. In Fig. 22 is shown a curve 
whose only defect is the sharp peak at 
S00 cycles. The effect of this peak will 
be to introduce a persistent ringing 
note into the reproduction which will 
be particularly annoying on the pas- 
sages of low volume. The effect will 
be that of someone continuously sound- 
ing a string of particularly discordant 
sleigh bells. 

While considerable space has been 
devoted in this article to the discus- 
sion of the technique of making re- 
sponse curves, the results of even the 
best made curves must be accepted 
with a degree of caution, and should 
always be checked by comparative ear 
tests on a variety of selections. In 
selecting records for ear tests, diversity 
in the character of music and voice 
should be the deciding factor, and not 
the testers personal taste in music. 















Same as Fig. 16 but with a differ- 
ent make pickup. 

In testing by ear for relative reproduc- 
tion of scratch noise, records should 
be used which have been played from 
ten to twenty times. The frequency of 
the scratch noise is generally higher 
on the outside of the record and the 
first few grooves before the actual re- 
cording starts are admirably suited 
for scratch determination. 

Determination of Relative 

The relative sensitivity of two pick- 
ups is a somewhat difficult thing to de- 
termine, but may be approximately 
evaluated in several different ways. 
If the response curve shows a rela- 
tively flat horizontal response in the 
middle range, say, from 500 to 2,000 
cycles, it is probably fair to take the 
voltage at these frequencies as a meas- 
ure of the sensitivity. It is for this 
reason that the writer prefers to ex- 
press the response curves in terms of 
voltage rather than of dbs, as it is 
then equally serviceable for both 

Another method of determining 
sensitivity from the curves is to deter- 
mine the average voltage throughout 
the useful range of frequencies, but 
this method generally results in a 
value which bears no identifiable re- 
lation to the apparent volume as heard 
by the ear. 

Probably the most reliable method, 
if care and time are taken in carrying 


FIG. 18 

Effect of tone arm on response 

it out, is that of comparative listening 
tests on a variety of selections and 
with two or more observers. This 
method has the advantage of giving 
directly useful comparative results, but 
is, of course, tedious. 

Permanent uniformity of perform- 
ance in an electromagnetic pickup de- 
pends primarily on three factors. First, 
the excellence of workmanship and 
simplicity of design: second, on the 
character of the material used for 
damping the motion of the moving sys- 
tem, and third, on the design and ma- 
terial of the permanent magnet. 

The first point can really only be 
determined by an inspection of the de- 
vice in the light of a broad mechani- 
cal experience. It is generally true . 
that the fewer the parts, and particu- 
larly moving parts, of any mechanical 
device, the greater the reliability. For- 
tunately, also, good workmanship is 
generally apparent on the surface in a 
device of this character. 

Where rubber is employed for damp- 
ing it is usually necessary to use it in 
such a manner that it is also relied 
upon, in whole or in part, for the cen- 
tering adjustment of the moving sys- 
tem. Such, for instance, is the case in 
the structure illustrated in Figs. 1 and 
2. Under these circumstances, the per- 
manence of the device and of its ad- 
justment are, at best, doubtful quanti- 
ties, depending upon the quality of the 
rubber employed, and the seasoning to 
which it has been subjected. There is. 
unfortunately, no adequate method of 
determining the life of the adjustment, 
other than observation over an ex- 
tended period. If life tests are under- 
taken to determine this point, the 
usual care should be exercised to sub- 
ject the device to all of the conditions 



a 3.5 







61 1 1 


^V o 

FIG. 19 

: '^\ 

• 1 

3 11 ^ 






o * 





Effect of weighted tone arm on 
response curve. 

Page 36 

Projection Engineering, October, 1929 







> \. 

F G.20 

"" "V 







Curve of commercial pickup which 
suppresses scratch noises. 

of temperature, moisture and vibration, 
which it is likely to meet with in 

In case no rubber or similar im- 
permanent material is used in a rela- 
tion of the mechanical system which 
can affect the adjustment, this source 
of doubt entirely disappears. 

The third factor affecting the life of 
the instrument, the permanent mag- 
net, can best be checked indirectly by 
means of the expression given previ- 
ously for stability of permanent mag- 
nets, which is here repeated for con- 
venience : 

Ag Li 

x > 70 

Lg Ai 

In this expression, A„ represents the 
area of the air gaps ; Lg, the length 
of the air gaps; Ai, the area of the 
cross section of the magnet, and Li, the 
length of the magnet. The value of 
the numeric on the right hand side of 
the above expression is for tungsten 
magnet steel, and this quantity should 
be reduced to 35 for steels containing 
15% cobalt. The four quantities above 
should be carefully measured in the 
actual instrument, and should satisfy 
the relationship for the particular steel 
which is used. In making the measure- 
ments of the gap length and areas, it 
should be kept in mind that there are 
four air gaps involved in the usual 
magnetic bridge type of construction, 
and the upper and lower pairs of gaps 
will usually be different in both length 
and area, and it must be remembered, 
in computing the effective gap reluc- 
tance that the reluctances of the upper 
and lower pairs are in parallel. 

Determination of Record Wear 

Probably the most satisfactory way 
to determine the relative record wear 
occasioned by two pickups of different 
designs would be to make microscopic 
examinations of records played by each 
of them, and some work of this kind 
has been undertaken, using wax rec- 
ords in order to speed up the effect, 
but the whole process is too tedious 
and expensive to be undertaken in the 
usual case. 

A reasonably close estimation of the 
effect can be secured by measurement 
and computation. As explained in de- 
tail previously, the wear on the side 
of the record groove at low frequencies, 
that is, at frequencies below the first 
natural period of the moving system, is 

occasioned by the effective mass of the 
armature transferred to the point of 
the stylus. This quantity may be easily 
calculated from a drawing of the arma- 
ture by means of the usual formulae 
to be found in mechanical handbooks. 
It should be noted in making these cal- 
culations that the effect is one of mass 
and not of weight, and, therefore, the 
weight of the armature used in the cal- 
culations must be divided by the grav- 
ity constant. The most convenient 
practice is to calculate the moment of 
inertia around the axis through the 
pivot of the armature and then to 
transfer the result to the point of the 

For determining the wear factor at 
high frequencies, it is most convenient 
to measure the actual deflection of the 
armature under a known force. A de- 
vice which the writer has found very 
convenient for this purpose is illus- 
trated in Fig. 23. In this figure, a 
pickup of usual design is shown in two 


z> 2.0 






— ■ — . 







FIG. 21 

Here, low-frequency response is 

poor and scratch noises are 


views and indicated by the numerals 
1 and 2, clamped in a U-shaped yoke 
3 by means of the clamp screws 4. In- 
serted into the needle holder in the end 
of the armature is the rod 5, of stiff 
tempered steel wire, such as a bicycle 
spoke. In order that no stray mag- 
netic field may leak down the rod, it is 
split, and the magnetic insulator 6, of 
bakelite, is inserted ; 7 in a permanent 
magnet rigidly mounted on the same 
platform as the yoke 3, and provided 
with a small V-shaped groove on one 




a '•= 


Hj 1.0 



FIG. 22 

Response curve of pickup with 

prominent peak at 800 cycles; this 

introduces a ringing noise. 

of its poles faces. Resting in this 
groove is a small iron piece 8, provided 
with a knife edge to engage the groove, 
and carrying a tiny mirror 10, as 
shown. The iron piece 8 is bent up at 
an angle along the edge away from 
the magnet face, which rests against 
the end of the rod 5, and is held firmly 
against it by the stray field provided 
by the magnet 7. A suitable source of 
light is arranged at 11, and the image 
of this source is reflected by the mir- 
ror on the scale 12. 

By means of this apparatus, very 
small deflections of the armature of 
the pickup device may be easily meas- 
ured, when the dimensions of the parts 
are known. 

A known force is applied to the rod 5 
at a point from the end of the armature 
equal to the distance which the needle 
projects from the armature, by means 
of the thread 13 running over the 
pulley 14, to the lower end of which is 
attached a known weight (not shown). 
In making these measurements, the 
pulley bearings should always be 
gently tapped to prevent friction re- 
ducing the amount of the force applied 
to the rod. 

In this manner, the ratio of the de-- 
flection to the force required to pro- 
duce it, may be directly measured, and 
the relative record wear which will be 
occasioned at low frequencies by two 
{Continued on page 38) 







\ —. RAYS M-^ H 





3'-6 n 

Arrangement for the determination of the wear factor of a pickup. 

Projection Engineering, October, 1929 

Page 87 

A Few Facts About Filters 

The Effect on Frequency of Series and Parallel Resonant Circuits 
By John F. Rider, Associate Editor 

DESPITE the great improvement 
in the design of loudspeakers, 
the performance of the aver- 
age loudspeaker-amplifier com- 
bination is still far from the ideal, this 
despite the most perfect impedance 
matching and so on. The reasons are 
numerous — too numerous to be men- 
tioned. As a result, measurements 
upon the system show definite "bumps" 
in the response curve. If these bumps 
or peaks are on the lower register, 
deliberate mismatching of the output 
transformer and the speaker or speak- 
ers, as the case may be, solves the 
difficulty in many cases. However, 
such an arrangement is unsuited when 


Series resonant or "rejector" filter. 

the peaks are at one or more inter- 
mediate frequencies between the upper 
and lower cut-off frequencies. Special 
filters are required and the best 
arrangement is the series resonant or 
rejector system shown in Fig. 1. L 
represents the inductance and C the 

Series and Parallel Resonance 

The action of the circuit when tuned 
to resonance is to offer a low impedance 
path to whatever is connected across L 
and C. Hence, if the circuit resonant 
to some frequency is connected across 
or in shunt with another path, the 
current due to a voltage will divide 
between the normal path and the re- 
sonant circuit in the ratio of the 

Many confuse series resonance with 
parallel resonance when the objective 
is the elimination of one frequency or 
the reduction of a peak. Reference 
to any text book wherein alternating 
current receives normal discussion will 
bring to light the distinct fact that the 
impedance relation at resonance is dis- 
tinctly different in the series resonant 
circuit and in the parallel resonant 
circuit. In the former, the impedance 
is zero, assuming an inductance with- 
out resistance, (which, however, is not 
found in practice) and in the parallel 
resonant circuit the impedance is sup- 
posedly infinite, once again assuming 
an inductance without resistance. 

Considering normal practice, the series 
resonant circuit offers a low impedance 
at resonance and the parallel resonant 
circuit offers a high impedance at 

Considering the action of the circuits 
off resonance, we again find a distinct 
difference between the two. The series 
circuit off resonance affords increasing 
impedance, with a preponderance of 
capacity reactance below the resonant 
frequency and a preponderance of in- 
ductive reactance above the resonant 
frequency. In the parallel resonant 
circuit, the circuit off resonance acts 
like an inductance below the resonant 
frequency and like a condenser above 
the resonant frequency. The signifi- 
cance of this condition can best be ex- 
plained by connecting each type of 
circuit across a loudspeaker winding 
fed from a variable oscillator. This 
illustration is not intended as a dis- 
cussion of electrical constants but 
rather to illustrate the effect and to 
attempt to show the action of each 
arrangement in the usual form of filter. 
This entire discussion is based upon 
the frequent erroneous mention of a 
parallel resonant circuit as a means 
of removing or minimizing a peak. 
This method has been described as 
being suitable for use as a scratch filter 
and also as a filter across the voice 
coils of dynamic speakers and across 
the windings of the magnetic speakers. 

Filter Circuits 

Suppose we consider the circuits 
shown in Fig. 2. Fig. 2 — A designates 
the series resonant circuit and Fig. 2 — 
B 2 the parallel resonant circuit across 
a 200-ohm winding. The frequency of 
the voltage is 1000 cycles. Let us 
assume that the normal current flow 
through the speaker impedance is .5 
ampere. In both cases the resultant 
impedance of the filter circuit will be 
in parallel with the speaker impedance 
and the currents in the two branches 
of the parallel circuit will be governed 
by the relative impedances. The value 
of L in each case is 100 millihenrys 
and the resistance of the winding is 3 
ohms d-c. The coils are of the honey- 

comb variety. Frequency at resonance is 

F = 

— — where L is in henrys and 
V L x C C in microfarads. 

With an arbitrary value of 100 milli- 
henrys for L, the value of C for reson- 
ance at 1000 cycles or, as a matter of 
fact, for any frequency, will be 

159.2 2 25,281 

C = or = .252 

F 2 x L 1,000,000 x .1 


(Although the resistance manifests an 
effect upon the resonant frequency in 
a parallel circuit, it can be neglected 
in this case and at audio frequencies 
because of its very low value with air 
core inductances.) 

In the case of the series circuit, the 
impedance at resonance will be 

Z= VR 2 + (Xl — Xc) 2 

Since the inductive reactance is equal 
to the capacity reactance, the react- 
ances cancel and Z = R, or 3 ohms. 
(The exact value of Xl is not equalled 
by the reactance of the .252 mf. con- 
denser, but if the fraction were carried 
out to a sufficient number of places 
the values of reactance would be equal. 
We also neglect the resistance of the 
condenser. ) 

It is evident that the impedance of 
the circuit is low and that the current 
in the circuit is high because 


and the value of Z is low. 

In the parallel resonant circuit, re- 
sonance is found when, like in the 
series circuit, Xl = Xc. In a parallel 
resonant circuit, the currents in the 
two branches are 180 degrees out of 
phase. At resonance the current in 
the inductive branch is equal to the 
current in the capacitative branch and 
the currents tend to neutralize each 
other. As a consequence, the impedance 
is high at resonance. Assuming a coil 
without resistance the impedance would 
be infinite. This is not possible be- 


Two filter cir- 
cuits. A is a 
series resonant 
filter and B, a 
parallel reson- 
ant filter. 


L C 









Page 38 

Projection Engineering, Octooer, 1929 

cause all coils possess resistance, and 
the impedance is finite. The impedance 
of the parallel tuned circuit at reso- 
nance may be classed as its effective 
resistance, since the controlling in- 
fluence is its resistance. We are, 
neglecting the effect of the resistance 
upon the frequency of resonance. The 
effective resistance or effective impe- 
dance may be determined by 


L 2 x (2pixF) : 


For the condition cited the effective 
resistance is 

.100 2 x 6283 2 


R ef( = 131,000 ohms (approximate) 

Considering the impedance of the 
speaker coil and the relative impe- 
dance of the respective resonant cir- 
cuits, it is evident that the series 
resonant circuit will influence the cur- 
rent in the speaker coil, whereas the 
parallel resonance will have no effect. 
It therefore stands to reason that the 
parallel resonant circuit is useless as 
a means of reducing a peak in a re- 
sponse curve under the circuit con- 
ditions shown in Fig. 2. 

Suppose that it is necessary to re- 
duce the current in the speaker coil to 
one-third of its original value at 1000 
cycles and the impedance of the coil 
is 200 ohms at that frequency. This 
means that the impedance of the filter 
must be one-half of the speaker coil 
impedance, or 100 ohms. The parallel 
resonant circuit is, of course, useless 
and it is necessary to increase the im- 
pedance of the series resonant circuit 
to 100 ohms. Part of this 100 ohms 
is in the coil to the extent of 3 ohms. 
The balance of 97 ohms will then be a 
series resistance as in Fig. 3. 

Effect of Circuits 

Now, relative to the effect of the 
two circuits at frequencies other than 





FIG. 3 


L g 





FIG. 4 

Series and parallel resonant cir- 
cuits with compensating resistors. 

resonance, the series combination pro- 
vides a high impedance circuit above 
or below resonance. For example, at 
800 cycles the reactance of the induc- 
tance is 

Xl = 2irxFxLor 
6.283 x 800 x .1 
502 ohms. 

The reactance of the condenser is 



2 7T x F x C mf 


= 790 ohms (approximate) 

Xl — Xc = 288 ohms ( we neglect the 
3 ohms in the 

The total impedance of the circuit in- 
clusive of the 97-ohm resistance is 

Z = 97 2 + (502- 
Z = 305 ohms. 

790) ; 

As is evident this value of impedance 
would still influence the current flow 
in the speaker coil, but such a con- 
dition is quite satisfactory because the 
shape of the response curve of a 
speaker is such that it extends over a 
range of at least 200 cycles each side 
of the peak frequency. The greater 
the condition of anti-resonance, the 
higher the impedance of the series 
resonant circuit and the less the effect 
of the filter circuit upon the speaker. 
In our case we operated at a difference 
of only 200 cycles. 

The action of the parallel resonant 
circuit is just the opposite. Below the 
resonant frequency the circuit acts like 
an inductance, because the major por- 
tion of the current in the circuit will 
flow through the inductance. As the 
reactances become balanced the greater 
the current flow in the parallel reso- 
nant circuit and the less the impedance 
since the total impedance would be 
Z = where I is equal to 



Xc Xl 

Above resonance the circuit would act 
like a condenser, because most of the 
current would flow through the con- 
denser and once again the impedance 
would decrease the more one prog- 
ressed from the state of resonance. 
Hence, the parallel resonant circuit 
would show the greatest effect off 
resonance and would cause a loss at 
all frequencies except at resonance. 

By inserting a resistance in series 
with the parallel resonant circuit as 
in Fig. 4, it is possible to maintain the 
impedance off resonance at a definite 
minimum and the circuit finds its ap- 
plication in the effort to equalize a 
system. In other words, to produce a 
rising characteristic rather than to 
remove a peak. This is accomplished 
by reducing the current at all fre- 
quencies other than the resonant 


(Continued from page 36) 
pickup of different designs may be 

It should be pointed out that the 
stiffness of a pickup armature cannot 
be estimated even approximately by 
attempting to estimate the force re- 
quired to move it by hand. The arma- 
ture in normal use, moves through only 
a very small angle, and may be very 
free throughout this range, and yet 
very stiff outside of the normal range 
of motion. 

The test methods outlined herein 
have been used by the writer and his 
staff in the investigation of pickup de- 
vices over a considerable period of 
time with entire success, and it is be- 
lieved that with proper attention to 
technique they will serve to accurately 
gauge the relative merits of the various 
designs of pickup devices. 


(Continued from page 26) 
it is a rather bulky affair. Then, there 
is the new screen, which we are told 
will eat up "at least a thousand dol- 
lars and probably much more," and, 
to cap all this, the theatre will have to 
close down during the installation of 
the new equipment according to present 

Two of the many reasons offered for 
Fox opening the Grandeur Pictures 
at the small old-fashioned Gaiety 
Theatre, rather than at the Roxy 
Theatre, or one of the other large Fox 
houses in the city, were — that Fox 
wanted to impress upon those seeing 
the Grandeur presentation that the 
system was suitable for use in the 
smaller theatres throughout the coun- 
try as well as the large modern ones— 
and the other excuse was that due to 
the fact that the projectors could not 

be installed between shows, it was 
necessary to use some theatre that was 
not given over to the continuous policy, 
like the Roxy. 

One thing is sure ; no matter what 
expense within reason that the ex- 
hibitor is put to in acquiring and in- 
stalling these new wide film projectors, 
he will have them installed sooner or 
later, for the same reason that most 
exhibitors installed sound-picture 
equipment; also, that these new wide 
film pictures which will enable pro- 
ducers to eliminate the cramped con- 
ception of situations and scenes so 
apparent in most of the screen produc- 
tions of today, and especially those 
where the screen image has been re- 
duced clue to the recording of sound on 
the film margin, will bring a steady 
line of cash paying customers to the 
box offices, of those theatres who offer 
them this better screen entertainment. 

Projection Engineering, October, 1929 

Page 39 


President's Address. 

Committee Reports. 
"The Human Equation in Sound Picture 

By Terry Kamsayb, Pathei Exchange, Inc. 

"Some Characteristics of Sound." 

A motion picture lecture. By Howard B. 

Santee, Electrical Research Products, Inc. 

"Reactions of the Public to the Talking 

By Harold B. Franklin, Fox West Coast 


"The Sound Film Situation in Europe." 

By M. D. Golden, Motion Picture Division, 

Department of Commerce. 

"Cinematography in Soviet Russia." 
By Leon Monosson, Amkino Corporation. 

"Sound Films for Surgical Instruction." 

By Dr. P. E. Truesdale, American Medical 

Association Gold Medalist. 

"The Trail of the Microphone." 
A motion picture lecture tour of the Holly- 
wood Sound Studios. 

"Some Fundamental Principles of Sound- 
Recording and Reproduction." 
By Wm. H. Opfenhauser, RCA Photophone. 

"The Principles of Sound Recording and 

Reproduction by the Variable Density 

Photographic Method." 

By D. Mackenzie. Electrical Research 

Products, Inc. 

"A Demonstration Talking Film." 
By Dr. Kinudon, General Electric Company. 

"Studio Acoustics and Microphone 


By J. P. Maxfield. Electrical Research 

Products, Inc. 

"Theatre Acoustics." 

By S. K. Wolfe. Electrical Research 

Products, Inc. 

"The Optics of Motion Picture Projection." 

By Prof. Arthur C. Hardy, Massachusetts 

Institute of Technology. 

"A New Method of Blocking Out Splices in 

Sound Film." 

By J. I. Crabtree and C. E. Ives, Eastman 

Kodak Company. 

"Photographic Characteristics of Sound Re- 
cording Film." 
By L. A. Jones and O. SIandvik, Eastman 
Kodak Company. 

"Characteristics of Loudspeakers for The- 

dt 1*6 TJSG " 

By D. G. Blattner. Bell Telephone Lab- 
oratories, Inc. 

"Lubrication of Sound Film." 

By J. I. Crabtree, D. Hindman. C. E. Ives 

and O. Sandvik, Eastman Kodak Co. 

"A Film Numbering Device for Cameras 

and Recorders." 

By M. W. Palmer, Paramount-Famous- 

Lasky Corporation. 

"Dimensional Analysis as an Aid to Mini- 
ature Cinematography." 
By G. F. Hutchins, General Electric Co. 

"The Film Perforation and Means for its 

By W. H. Carson, Agfa Ansco Corporation. 

"Camera Mechanisms — Ancient and 

By Arthur S. Newman, London, England. 

'Early History of Motion Picture Cameras 

for Film. Wider Than 35 m.m." 

By Carl Louis Gregory. 

"Possibilities and Problems of the Wide 


By Lorenzo DelRiccio, Paramount- 

Famous-Lasky Corporation. 

"Rectangle Proportions in Pictorial 

By L. A. Jones, Eastman Kodak Company. 

"Wide Films and Standardization." 

By A. S. Howell & J. A. Dubray, Bell & 

Howell Company. 

"The Wide Film from the Recording 


By C. A. Tutkill, Paramount-Famous- 

Lasky Corporation. 

"Artistic Considerations in Sound Film 


By Joe W. Coffman. Carpenter-Goldman 

Laboratories, Inc. 

"A Rapid Method of Determining the 

Degreee of Exhaustion of a Developer." 

By M. L. Dundon, G. H. Brown and J. G. 

Capstaff, Eastman Kodak Company. 

"Burn Out Phenomenon of the Tungsten 

By Gorton T. Fonda, General Electric Co. 

"Water Cooling of Incandescent Lamns." 
By Dr. Newell T. Gordon, General Elec- 
tric Company. 

"Radiation Characteristics of Two Mercury 

By A. C. Downes, National Carbon Co. 

"Some Properties of Chrome Alum Fixing 


By J. I. Crabtree and J. F. Ross, Eastman 

Kodak Company. 


The Bureau of Navigation has recentlv 
had several requests from naval activities 
ashore and afloat regarding installation of 
talking-picture devices aboard ships and 
at stations of the Navy. 

For the information of all concerned the 
Bureau desires it to be known that both 
engineering and navigation are now and 
have been for two years past, actively in- 
vestigating this subiect. At present writ- 
ing, none of the machines on the market 
are especially well adapted for Navy use 
and the present methods of sound recording 
make the life of the film only about one- 
tenth the life of the silent film. 

This fact, together with the additional 
cost of "talkie" film, makes the present 
price of 'talkie'' films almost prohibitive to 
the Navy. New methods of sound recording 
and new types of sound projectors better 
adapted to Navy use, are in the process of 
development and the Bureau's policy is to 
await further developments while at the 
time making experiments and keeping 
abreast of present developments. 

Silent films suitable for Nnvy use are still 
being produced, but the limited number 
makes necessary the reduction of the supply 
of programs to the fleets. To maintain the 
fleets with sufficient programs for the av- 
erage exhibition of 28 programs per month, 
requires the purchase of 30 nrograms a 
month, and this, at present writing, is im- 
possible unless a lower standard of quality 
of programs is accepted. The Navy motion 
picture service will probably, bv aid of the 
foreign market, be able to obtain 20 pro- 
grams a month during the coming year, ne- 
cessitating an increase of 30 per cent in 
"reshows" or a reduction in the number of 
programs exhibited each month by the 


Production on the Pacent sound-on-film 
attachment is going forward at two fac- 
tories to supply existing orders and meet 
increased demand for sound reproducers for 
the early fall season. 

Mr. Pacent said that over 300 orders for 
the combination disc and sound-on-film sys- 
tems manufactured by his company are 
now on hand. He declared that the re- 
sults obtained by the new film attachment 
in actual performance at several theatres 
exceeded even the optimistic hopes of 
officials of the company. Features of the 
device which! he said have proved especially 
satisfactory to operators are the special 
optical system, new type photoelectric cell 
and elimination of all batteries. 


The Projection Advisory Council will 
give a luncheon to William F. Canavan, 
International President of the I. A. T. S. E. 
and M. P. M. O., at the Hotel Astor at 
1 p. m., Thursday, November 14th. Mr. 
Canavan will deliver a talk on "Projec- 
tion and the Projectionist." 



So little is understood and so much is 
misunderstood regarding television that a 
booklet entitled "Television — The Eye of 
Radio," is most welcome at this time. 
Under this title, the Jenkins Television 
Corporation of Jersey City, N. J., has pub- 
lished an attractive booklet of 32 pages 
and cover, which contains a conservative, 
interesting, readily understood discussion 
of just what television is, what has been 
done so far, what is being done for the 
future, and why the television experiment 
is about to develop into the television in- 
dustry. The booklet contains photographs 
and descriptions of the eqiu.pment about to 
be introduced for home use, as well asi the 
television studio and transmitting equip- 
ment. A copy is free for the asking. 


The Samson Electric Company of Canton, 
Massachusetts has recently published an 
interesting sixteen page bulletin, giving the 
specifications of PAM amplifiers for nearly 
every type of installation. Complete me- 
chanical and electrical characteristics of 
the various amplifiers are included and a 
number of representative installations are 

Many types of PAM amplifiers are shown, 
including two and three stage amplifiers, 
utilizing 210's, 250's and 245's in the 
last audio stage. Several microphone 
amplifiers are described and also a special 
double channel amplifier, designed to fill 
the needs of an installation where a spare 
amplifier is instantly available, in case a 
minor defect develops in the one that is 
being used steadily. 

. The installation at the Marigold Ball- 
room at Minneapolis is particularly intei- 
esting. The use of muted instruments 
lessened the power of the music to pene- 
trate to the distant corners of the large 
room. This difficulty was entirely over- 
come through the installation of a PAM 
amplifier and a group address system. The 
orchestra music is now picked up by a 
microphone which delivers it through the 
PAM installation to loudspeakers placed in 
remote corners. 

The new Samson bulletin will be sent 
free of charge to anyone interested, pro- 
vided stamps are enclosed to cover postage. 

Page 40 

Projection Engineering, Octooer, 1929 


It is announced that a radio picture re- 
ceiver will, in the near future, lie marketed 
in Australia by Television and Radio Labor- 
atories Pty, Ltd., of 94 Queen Street, Mel- 
bourne. The receiver is simple in construc- 
tion and thoroughly reliable in operation, 
and as efficient synchronism is obtained 
without the use of a magnetic clutch, the 
cost of construction is considerably less 
than is the case with other similar ma- 

It is also the intention of the T. R. L. 
Co. to sell sets of parts to enable home con- 
structors to make these machines them- 
selves. Portions that cannot be made by 
the average amateur, such as gear wheels 
and leadscrews, will be included in these 

It now seems certain thnt the Govern- 
ment will provide or permit the operation 
of picture services by broadcast in the near 

The receiving unit of the T. R. L. Co. is 
simple. It is driven by a spring motor 
similar to that used in a phonograph, and 
all the working parts are mounted above 
the base. The machine is constructed of 
aluminum, and working parts are of steel. 

Synchronism is achieved with a double 
tripping mechanism, which partially re- 
leases drum upon commencement of synch- 
ronizing impulse, and completes the release 
upon its cessation. 

A potentiometer for control of density, 
milliammeter and removable relay of the 
plug-in type are fitted upon base at rear 
of machine. 

The last tube of any good receiver can 
be used to rectify the received current if 
suitably biased, but a self contained recti- 
fying panel with suitable bias controls and 
milliammeter permitting the receiver to be 
used with any set without alteration is also 
being made available. 

Pictures are received upon absorbent 
paper that has previously been impregnated 
with a special solution, that will be re- 
tailed at a small cost. Prints, when dry are 
of reddish brown, but may, if desired, be 
quickly toned to a purple-black. 

Prints made upon the T.R.L. machines 
will be called Radiostats. 

with the Boston Edison Company, he joined 
the then newly organized Raytheon Com- 


Announcement has been received that Mr. 
D. E. Replogle, formerly Sales Engineer in 
the Product Development Division of the 
National Carbon Co., has been appointed 
Assistant to the President, and General 
Manager of the Jenkins Television Corpora- 

Mr. Replogle came from the Raytheon 
Manufacturing Company, the control of pro- 
duction and sales of whose products was 
recently acquired by the National Carbon 
Company. There, since its early organiza- 
tion, Mr. Replogle was very closely associ- 
ated with the development and technical 
merchandising of all Raytheon products, at 
first working on circuit development and 
directing a customer technical service lab- 
oratory. He also directed publicity and 
edited the Raytheon technical bulletins. He 
has always been keenly interested in nevJ 
developments in the communication field, 
especially in television and was responsible 
for production of the Raytheon television 
products, and at present is Chairman of the 
Television Committee of the Radio Manu- 
facturers Association. 

His first interest in radio, or wireless as 
it was then called, goes back to the early 
days of the science. After graduating from 
Pacific College near Portland. Oregon, he 
entered the service of the United States 
Government, taking charge of an Eskimo 
reservation at Noocvik, Alaska, 200 miles 
due north of Nome and forty miles north 
of the Arctic Circle. Communication with 
outside civilization required two months. 
Mr. Replogle persuaded the Government to 
purchase a simple wireless equipment, which 
he installed, thereby establishing the 
farthest north station on the American 
continent. From the first the station was a 
success. News was received from all parts 
of the world, and a small newspaper which 
was made up each day, was carried by 
native hunters to the few white prospectors 
and teachers in the northern wilds. Dur- 
ing the time Stefansson, the Arctic ex- 
plorer, was sick at Herschel Island, his 
only news from the world came through 
these sheets. 

Mr. Replogle left the Government service 
in 1920, and entered the Massachusetts In- 
stitute of Technology, where he studied 
Electrical Engineering, graduating in 1925, 
with Bachelor and Master's degrees. Dur- 
ing his course he was associated with 
private radio interests around Boston and 
upon graduating, after a short time spent 


Phono-Kinema. a corporation recently 
formed in New York, has acquired a license 
to manufacture sound-on-film apparatus in 
the United States and Canada under the 
patents controlled by Theodore Nakken. 
This move will enable the company to in- 
clude both disc and sound-on-film with in- 

Deliveries of the dual system are at pres- 
ent scheduled for four weeks after receipt 
and acceptance of order and reproducers 
are priced at $2,950 installed. Amplifica- 
tion, monitor, control board and speakers 
are included in this figure but not the cost 
of wiring between stage and booth. Ex- 
clusive of amplification, monitor, control 
board and speakers, sound heads are listed 
at $1,750 each per units of two. All equip- 
ment is sold outright, without service 
charge and a guarantee of patent protec- 

The Nakken patents cover means of audio 
amplification, sound gates, monitoring and 
recording systems, listing but a few. 


Numerous instances have recently been 
noted where prominent business houses, in 
order to cash in on the popularity of their 
trade-marked merchandise and to definitely 
tie-up the name of the product and the 
manufacturing organization in the minds of 
the buying public, have changed their cor- 
porate names to the name of their trade- 
marked product. 

It is this process of natural development, 
thrust upon it, it might be said, bv the 
trade's acceptance of the product, that has 
caused the Ultraphonic Products Co., New 
York City, to change its name to Upco 
Products Corp. 

Approximately a year ago the Ultra- 
phonic Products Co. was formed by A. 
Borsuk, who previously had twelve years' 
experience in the production of acoustic 
reproducers. The name Upco was selected 
as the trade-mark to designate the product 
which name, it may be seen, was formed 
by the initial letters of the corporate name. 


The office and factory of Jenkins & Adair, 
Inc., are moving to a new and strictly 
modern one-story plant, located at 3333 
Belmont Avenue, Chicago 

The new Jenkins & Adair plant in 

The new building will provide manufac- 
turing facilities far superior to those which 
the company has had since its inception 
six years ago. The new plant will also 
permit a substantial increase in production. 

The basis of the business of Jenkins & 
Adair is the production of special trans- 
formers and retard coils, condenser trans- 
mitters, broadcast and recording amplifiers, 
mixing controls and gain controls. 


Recommendations for a correlation of 
practice on projector apertures at theatres 
where special apertures are used to restore 
the full screen proportion from sound-on- 
film pictures were made in the form of a 
resolution adopted at a joint meeting of the 
Academy of Motion Picture Arts and 
Sciences Technicians' Branch, the Ameri- 
can Society of Cinematographers. and the 
Los Angeles Chapters of the Society of 
Motion Picture Engineers and the Ameri- 
can Projection Society, held at the Roose- 
velt Hotel, Hollywood, on September 19. 

The resolution, based on the report of 
a joint committee which conducted a na- 
tional survey of theatre chains, recom- 
mends that theatres making a practice of 
restoring sound film to full screen pro- 
portions, by means of special devices that 
mat off the top and bottom of the picture, 
do so by the use of an aperture whose 

size would be 0.600 by 0.800 inches on 
the basis of projection on the level, the 
horizontal center of the aperture coincid- 
ing with that of the S.M.P.E. standard 

The technical societies jointly recom- 
mend that studios compose scenes with an 
area of 0.620 by 0.835 inches in produc- 
ing sound-on-film pictures so that in the- 
atres which use a smaller aperture the 
heads and feet of characters will not be 
matted off. 

Joint committees were authorized to in- 
vestigate and make recommendations on 
release print standardization screen illumi- 
nation. The present variation in the length 
and marking of the leaders on prints from 
different studios and laboratories and the 
difficulty encountered by projectionists 
when no silent frames are allowed at the 
beginning and ends of reels for changeover 
will be included in the investigation by 
the committee. 


Charles Gowie, manager of the Charles 
I. Newton Co., manufacturers of stage light- 
ing equipment, announces the removal of 
the factory to larger quarters at 253 W. 
14th Street, New York City. 


The demand for General Amplifiers has 
been increasing so rapidly that the company 
has recently appointed the following new 
representatives : 

Mr. Walter W. Boes, 622 Broadway, Cin- 
cinnati, Ohio, who will cover the territory 
of Southern Ohio and Northern Kentucky, 
Mr. G. J. Spencer, 29 Steward Street, De- 
troit, Michigan, who will handle the General 
Amplifier line in and around Detroit, and 
Mr. V. A. Hendrickson, c/o Martin-Copeland 
Company, 37 Maiden Lane, New York City, 
who will cover the territory of Metropolitan 
New York. Philadelphia, New Jersey and 
Southern California. 


The requirements of talking pictures have 
necessitated the doubling by the Victor 
Talking Machine Co. of its manufacturing 
facilities at Hollywood, Calif., at a cost of 

The Victor Company has awarded the 
Austin Co. of California the contract for 
design and construction of a duplicate of 
and an extension to the present plant of 
the Victor Company at Hollywood, which 
was designed and constructed by the Austin 
Co. of California a year ago. The new 
building is to be completed about the middle 
of December. 

According to C. H. Hall, Pacific Coast 
manager of the Victor Company, the new 
building will be used exclusively for the 
manufacture of records for Hollywood 

The Austin Co. of California and its 
engineering representative, R. E. Ward, 
have long been associated with the develop- 
ment of motion pictures. A few years ago 
the company designed and constructed an 
entire film city for First National Pictures, 
Inc., at Burbank, Calif., at a cost of $2,000,- 
000. Its contribution to the progress of 
talking pictures through the perfection of 
sound-proof stages is typified by recently 
completed studios for Metro-Goldwyn-Mayer 
and Columbia Pictures, Inc., at Los Angeles 
for talking pictures. 


Within 30 days, the television broad- 
casting stations, known as the W2XCP, be- 
ing erected by the Freed Eisemann Radio 
Corporation, will begin to broadcast regular 
programs from the Allwood. N. J., plant of 
the Freed Eisemann Radio Corporation. At 
the present time, the antenna has been 
erected, and the equipment is already radi- 
ating energy during the preliminary tests 
which are being made prior to the broad- 
casting of regular programs. Both wave- 
lengths granted to the corporation, 2000 to 
2100 kilocycles and 2850 to 2980 kilocycles, 
will be utilized. 

It is expected that the Dodge Twins, 
noted Broadway stars, and many other 
theatrical luminaries, together with the 
Governor of New Jersey will be present at 
the inauguration of programs from this 
station. While the station has been built 
and will be run for the purpose of develop- 
ing television apparatus, it will also enrich 
the .programs available to the group of 
television enthusiasts who are building and 
operating their own receivers at the present 

Projection Engineering, October, 1921) 

Page J/1 


A powerful, but compact dynamic speaker 
unit of unique construction has been placed 
on the market by the Racon Electric Com- 
pany, 18 Washington Place, New York 
City. The unit is called the New Racon 
"Baby Giant" and incorporates a number 
of important improvements in its design. 

One of the features of the "Baby Giant" 
is the new type diaphragm, made of metal 
and cloth. This is of such extreme light- 
ness that it has practically no inertia. In 
fact, a jewelers scale is necessary to weigh 
it. The voice coil is wound with alum- 
inum wire to keep the entire unit light. 
It has an impedance of 10 ohms. Flexi- 
ble leads are used between the voice coil 
and the binding posts. 

The diaphragm is dome-shaped, utilizing 
the principle of the "arch," which is the 
strongest form of construction known. An 
improved method of suspension is used in 
this diaphragm. The outer portion, which 
is clamped at several points, is made of 
chemically treated cloth. With this new 
type of suspension, extreme movements of 
the diaphragm are possible, without danger 
of cracking. The diaphragm rides up and 
down with a piston-like motion and hence 
it is impossible for it to get out of ad- 
justment. A brass screen prevents dust 
and other foreign particles from falling 
onto the diaphragm. The case of the unit 
is made of a special magnetic steel, com- 
bining high flux density with light weight. 

The new Racon unit weighs only 11% 
pounds, being one of the lightest and most 
powerful dynamic units on the market. It 
will handle an undistorted output of 30 
watts without rattling and even at enorm- 
ous volume, the tone quality is clear and 
brilliant. The response range is wide, 
passing all the desired bass notes but also 
passing the higher frequencies, so that 
speech is clear and distinct. The unit is 
made for 110 volt a-c. operation and also 
for use with a 6-volt battery. It has a 
field consumption of one ampere. 

New Racon Dynamic Unit. 

The "Baby Giant" derives its name from 
the fact that it combines compactness with 
great power. It is 5% inches high by 4% 
inches in diameter. These are overall di- 
mensions. The body of the unit is only 4 
inches in diameter. 

The new Racon unit is suitable for' 
home radio use, for public address systems, 
for talking motion pictures, and is adapt- 
able for theatre or outdoor use. The list 
price of the unit is $50. 


The Universal Microphone Co., 219 North 
Market St., Inglewood, Calif., have intro- 
duced a new model condenser microphone 
having a number of unusual features. Re- 
ferring to the illustration, the single stage 
amplifier is housed in the casing to which 
the microphone proper is attached. This 
amplifier employs a single 224 screen-grid 
tube, arrangements being made to light the 
filament from a six-volt storage battery. 
The microphone case also includes an Im- 
pedance matching transformer, in the out- 
put circuit of the amplifier. 

A potential of 200 volts is maintained on 
the condenser. 

New Universal Condenser 

All electrical connections are made 
through the special detachable 25-foot cable 

The price of the Universal condenser 
microphone, without swivel, is $250 with 
floor stand, $340. 


This addition to the well known Electrad 
line of radio resistances and voltage con- 
trols is recommended particularly for use 
as a plate resistor, multipliers for volt- 
meters and general laboratory work. 

The finest grade of Nichrome resistance 
wire is wound in generously insulated 
layers around a selected refractory tube. 

Electrad Layer-Wound Resistance. 

The entire unit is covered with a heavy 
coating of moisture-proof enamel of unusual 
elasticity, baked on at only 400 degrees to 
prevent loosened connections and fractured 
wire. Contact bands and soldering lugs are 
of Monel Metal. The lugs are solder-dipped 
for easy soldering. All parts expand 
equally under load. 

The overall length of the unit is 2 inches, 
with a maximum outside diameter of % 
inches. It is made with resistance ratings 
from 10,000 to 250,000 ohms and priced from 
$1.50 to $5.00. 


The Trimm Radio Manufacturing Com- 
pany, Chicago, Illinois, has developed a 
dynamic chassis that combines wide range 
with true tone fidelity and furnishes ex- 
treme volume with mellowness. Blasting 
and distortion are entirely eliminated. 

The Chassis is obtainable in two models — ■ 
Model D100 and DV102. 

D100 operates from a chassis of the 
alternating-current type where the output 
energy is supplied by the conventional type 
of power amplifier tubes in push-pull, this 
energy being fed through an output trans- 
former which matches the voice coil : and 
where the power pack supplies direct cur- 
rent for energizing the field coil. 

DV102, illustrated, is provided with an 
output transformer which matches the con- 
ventional type of power amplifier tubes and 
the voice coil. 

New Trimm dynamic speaker 


The Amplion Corporation of America, 133 
W. 21st St., New York City, announces a 
new fader for accurate volume control of 
disc and film track reproduction. 

The new Amplion constant impedance 
fader regulates the volume of the sound 
without altering the frequency character- 
istic of the phonograph pickup or the input 
transformer to which it is connected. This 
fader maintains a constant impedance on 
the pickup to the input transformer, re- 
gardless of the volume at which it is set. 
Through this new method, the fine harmon- 
ics are preserved throughout the reproduc- 
ing apparatus, making possible a decided 
improvement in the definition of both or- 
chestration and voice. 


A "super-dynamic" speaker has just been 
announced by the Stevens Manufacturing 
Corporation, Newark, N. J. This dynamic 
is designed for outdoor, auditorium and 
theatre use, and is especially suited for the 

The Stevens super-dynamic speaker is 
capable of handling an input of 14 watts, 
with an exceptionally smooth frequency 
response curve from 40 to 6000 cycles. The 
entire assembly is mounted on an extra- 
heavy chassis, including the transformer, 
choke and condenser, for operation on , 110- 
volt, 60-cycle a-c. supply. The speaker' em- 
ploys a 14-inch cone of the cubical parabola 
type made of the well-known Burtex ma- 
terial. The supporting member is integral 
with the cone, making them practically one. 

The special features of this super-dynamic 
speaker are several, beginning with a low- 
impedance voice coil of large diameter and 
few turns. This coil is supported at the 


Projection Engineering, Octooer, 1929 

center by a member attached to the pole 
piece. This flexing member is in turn 
integral with the diaphragm. The field coil 
is designed to provide a very high flux 
density, since there are 3,500 ampere turns 
around the center pole. The field excita- 
tion also presents a new development, with 
its 281 type rectifier tube applying 300 volts 
at 100 milliamperes to the field coil. Great 
care has been taken in the development of 
the voice coil transformer, the impedance 
of which is accurately matched to the input 
of the power tube and the output to the 
voice coil. Special attention has been paid 
to the materials used for the pot magnet 
and pole pieces. Also, the method of 
mounting insures correct balance and drive. 
With 120,000 lines per square inch of mag- 
netic flux, this speaker is one of the most 
powerful dynamic speakers of today. 

the vitreous enamel type and in manufac- 
ture, are kept within a tolerance of plus 
or minus 10%. 


Introduction of a new synchronous disc 
reproducer incorporating several novel fea- 
tures has been made by the Allectric 
Synchronization Machine Corp., of New 
York, with the "Allectric" unit manufac- 
tured by that company. 

The entire synchonization by means of 
this unit is accomplished by electric con- 
trol. The turntables may be located in 
any part of the theatre, as they are op- 
erated in electrical synchronization with 
the projector. This feature, it is claimed, 
will enable theatres to operate with sound 
without the added expense of increased pro- 
jection room personnel. The projectionist, 
provided the turnables are located in the 
pit, or anywhere outside the booth, has 
merely to set his film to start on the start- 
ing mark. The synchronized discs, similarly 
are set to the starting marks, and both 
projector and turntables are put into op- 
eration by the starting of the projectors. 
There, also, is a resynchronization device, 
operated electrically from the turntables, 
which will compensate, it is said, for loss 
of synchronization through improperly 
patched film or the jumping of the pick- 
up needle a groove on the disc. By this 
device the operator at the turntables is 
enabled to bring the screen action and the 
sound back into synchronization almost im- 
mediately merely by throwing a lever to 
the right or the left according as required 
to speed up the action, or speed up the 
sound to bring both into matched operation. 

The unit has a double channel amplifier, 
to provide an emergency amplifier unit in 
the event of tube or other trouble develop- 
ing during the use of one of the channels. 
The installation provides for the addition 
of a variable speed motor on the projector, 
wiring from this to the turntable and am- 
plifier unit, assembled in one cabinet, and 
speaker horns behind the screen. 


Hardwick, Hindle, Inc., 215 Emmet St., 
Newark, N. J., have introduced a new type 
fader, known as the HH Volume Fader. 

This new fader is so designed that it is 
possible to place it in the most convenient 
location, even outside the projection booth, 
if desirable. This is made possible through 
the use of a coupling shaft, to which is 
attached two drum-type control dials. The 
shaft is supplied in any desired length, and 
with a flexible coupling when required. 

It is not necessary that the dials be 
placed as shown in the illustration ; if de- 
sired they can both be mounted on either 
side of the coupling shaft. 

The cover of the HH Fader can be re- 
moved by taking out but three screws near 
the top, thus making inspection or repair 
an easy task. 

The resistors used in this fader are of 


The Weber Machine Corporation, of Roch- 
ester, N. Y., have announced their latest 
model synchronized turntable. The drive 
has a spring suspension and there is a 
flexible coupling arrangement incorporated 

The Weber Syncrodisk. 

to take care of possible misalignment. It 
is said that the machine can be attached 
to a projector in fifteen minutes. 

Ball bearings are employed throughout 
and all working parts are submerged in oil. 


An automatic rewind, incorporating fea- 
tures that are designed to give it special 
efficiency in the handling of sound films, 
lias been developed by the Gold-E Manufac- 
turing Company, 2013 LeMoyne Street, Chi- 
cago. The new device is being marketed 
by the National Theatre Supply Company. 

The Gold-E rewind is made of gray iron 
and is cast in one piece with bearings and 
legs over-sized and well ribbed. The body 
and bearings are mounted at an angle 
which is said to solve the problem of keep- 
ing the reel in mesh with driving pin, 
eliminating rotating springs and dangers 
of friction, heat and fire. The inside of the 
body is lined with sound absorbing felt. 

The door of the new rewinder is of alumi- 
num, cast in one piece and beaded on the 
inside to make the device fire tight and 

dished toward each center for rigidity and 
strength. An important feature is the use 
of a patented mercury tube lock which is 
locked in neutral position as soon as the 
door is open, thus breaking the circuit. 
Adjustable friction for any desired tension 
is provided for through the accurately ma- 
chined brake and asbestos lined drum. 
Power is furnished by a Janette motor 
mounted in cast recess in housing and 
driving through endless "V" belt. 

Another feature of the device is a gauge 
pointer which slides on a shaft fitted at 
the bottom of the case which enables the 
projectionist to straighten out any reel. 

Improvements, including a new waffle 
type cooling plate that dissipates heat and 
prevents film buckling and tension gate 
warping have also been made. 

The National Gold-E Rewind has been 
approved by the National Board of Fire 


A new development in talking picture 
speakers employs the entire screen as the 
talking surface to reproduce amplified 
sound. This radical development, along 
lines that have been discussed by engineers 
for some time as possibly the ideal method 
for reproducing the talking films, is being 
manufactured by The Potter Company, 
North Chicago, well known in the radio 
field as the makers of Potter by-pass con- 
densers and other products. 

The new speaker is really a condenser, 
or an electrostatic speaker, in which four 
condensers are mounted directly on the 
screen used for the projected pictures, and 
thus does away with horns or other types 
of reproducers. 

Among the many advantages claimed for 
the talking screen as a sound reproducer 
are that, due to this entire large surface 
vibration a huge flat wave of sound is pro- 
duced, and that the speaker has carrying 
and penetrating powers far beyond the 
point of projection, a result of the large 
volume of air that is moved. 

From the standpoint of operation, the 
talking screen eliminates need for the often 
elaborate provisions necessary to clear the 
stage of horns or other types of speakers, 
when vaudeville or presentation numbers 
requiring full stage space are offered. The 
speaking screen requires no more room than 
the ordinary silent projection screen, the 
projection surface and speaker being com- 
bined and mounted on a frame for car- 
riage to the loft like a drop or curtain. 

The condenser speaker consists of two 
plates held at a certain distance apart by 
a high dielectric of extreme thinness. One 
plate is a metal foil sheet placed directly 
on the dielectric sheet which, incidentally, 
is of such a fabric and insulation material 
as to be without a natural period of vibra- 
tion of its own, yet allowed to carry a 
charge over the complete surface as does 
the front sheet. A polarizing voltage to 
hold the two sheets in as close a con- 
tact to each other as possible is placed 
across them, so that output of the ampli- 
fier connected to this polarizing line super- 
imposes the voice and music frequencies 
on to the leads of the speaker. These 
voice and music frequencies vibrate the 
two plates electrically with full wave 

Unlike other speakers that have point 
projection that depend upon increasing their 
width of projection by throwing these 
points, or beams, of sound out at angles, 
the condenser speaker throws its sound 
in practically a flat wave, parallel to the 
surface of the speaker and extending in 
length of projection as it travels from the 

For motion picture application there are 
three ways of installing the condenser 
speaker. The ideal way is to build the 
entire screen as the talking surface. A 
second method is to provide a mask for 
a column of speakers with one front sur- 
face each side of the projecting screen and 
a column at the bottom. The horizontal 
column, at bottom, projects flat wave vibra- 
tions directly at the main floor audience, 
covering the auditorium from side to side, 
while the vertical columns not only cover 
the sides of the house but the balconies 
as well. A third method is to install in- 
dividual speakers back of a porous screen. 
The disadvantage of the latter method is 
that the air column being flat and wide is 
slightly held back in passing through the 
porous screen. 

The H H Volume Fader. 


Powers Cinephone, through its president, 
P. A. Powers, announces to the trade the 
new "De Luxe" 1930 Powers Cinephone 
sound reproducer. 

The De Luxe model is in three separate 
forms ; disc, sound-on-film, or a combina- 

Projection Engineering, Octooer, 1929 

Page 43 






(The subscription 
rate for individual 
subscribers is $2.00 a 



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tive, purchasing agent, production mana- 
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Page U 

Projection Engineering, Oetooer, 1929 

tion of both systems. Standardization of 
units which permit theatres, installing only 
the disc equipment to add the sound-on-film 
attachment at any time, is claimed as one 
of the features of the new model. Also, 
those installing sound-on-film equipment 
may at any time add the disc attachment 
without discarding any part of equipment 
already installed. 

Other changes named by the company 
include the motor drive as a separate unit, 
devised to overcome vibrations and elimi- 
nate breakage in photoelectric cells and ex- 
citer lamps ; the sound-on-film attachment 
has larger sprockets from which it is 
claimed greater smoothness and more even 
tone in reproduction is obtained ; all 
manual controls have been simplified ; gear- 
ings silenced by enclosing in grease-filled 
housing, with automatic lubrication ; turn- 
table for disc attachment designed so that 
discs fit in protected recess ; amplifiers with 
circuit-protectors guarding all main ar- 
teries to prevent destructive voltage fluctua- 
tion, and entire design constructed to make 
every part easily accessible to the operator. 


For television and other applications 
calling for photoelectric or light-sensitive 
cells, the National Carbon Company, Inc., 
New York City, now announces a compre- 
hensive line of Raytheon Poto Crlls. These 
cells are made in the hard-vacuum and the 
gas-filled types, as well as in bulb and 
tubular shapes. 

Eveready Raytheon Foto Cell. 

The hard-vacuum Poto Cell has the char- 
acteristics of instantaneous response — no 
lag ; response directly proportional to illu- 
mination ; maximum photo-active surface ; 
permanent characteristics ; no leakage or 
"dark current." The gas-filled Foto Cell has 
the characteristics of super-sensitivity ; in- 
stantaneous response — no lag : response di- 
rectly proportional to illumination ; no dam- 
aging effect from ionization ; low operating 
voltage ; no leakage or "dark current.' 

The Poto Cells are available in tvip 
spherical bulb types and three tubular 
types to meet a wide variety of uses in 
television, daylight recording, photometer, 
fire alarm system, laboratory, experimental 
and other applications. 


Mr. Prank Reichmann, Vice-President and 
Chief Engineer of the Oxford Radio Corpo- 
ration announces an addition to their 
regular line of Dynamic Speakers of the 
Auditorium Series which speakers have an 
overall height of 12% inches and a dia- 
phragm measuring 11% inches. With these 
models, the Oxford line now includes 
standard speakers with 8-inch, 10-inch and 
11% -inch diaphragms. 

This Auditorium Series is designed es- 
pecially for theatre work and for use in 
DeLuxe, high-priced sets where a speaker 
of exceptionally large size is desired. The 
one-piece cloth diaphragm which is metal- 
lized by a special process found only in 
Oxford Speakers is puncture proof with a 
controlled edge giving superior quality at 
all frequencies. 


The Upco Products Corp., 270 Lafayette 
St., New York City, are marketing a new 
electric pickup designed especially for use 
in connection with motion picture sound 

It is stated that the Upco Pickup has a 
uniform frequency response from 5,000 to 
50 cycles. 

The Upco Electric Pickup. 

A unique feature of this pickup is the 
special ball-bearing yoke action and ball- 
seated base pivot. This arrangement tends 
to decrease the record wear factor of the 

The standard model of the Upco Pickup, 
as shown in the accompanying illustration, 
is supplied with a built-in volume control. 
Other models, for theatre use, are supplied 
without the volume control and are de- 
signed to be used with standard type faders. 


A fire extinguishing apparatus applicable 
to motion picture projectors has been in- 
vented to use carbon tetrachloride in gas 
form as the extinguishing medium. The in- 
ventor is Charles A. Helm of Cleveland, 
where he is connected with Loew's Allen 
Theatre. The inventor states that although 
the device is intended for general use, he 
believes it particularly applicable in con- 
junction with sound equipment. 

In mounting this device, it is preferable 
to remove the heat shield from the pro- 
jector head, and for this, a device for 
volatilizing the carbon tetrachloride is sub- 
stituted, the device being of the size and 
shape of the shield. 

The volatilizing element comprises a thin 
rectangular-shaped casting provided with a 
central aperture for light. This device 
holds a container for the carbon liquid, 
under pressure. A conduit extends from 
the container to an inlet in the volitilizing 
element and has a valve to be operated by 
a lever. When the film catches on fire, a 
pull of the lever opens the valve, lets the 
carbon tetrachloride into the volatilizing 
element, where it is vaporized by the heit 
created by the light, and this gas is forced 
out upon the film and into the magazines, 
smothering the fire. 


The Film Inspection Machine Co. of 630 
Ninth Avenue, New York, is now putting 
on the market a film inspection machine 
having some new features to meet the new 
conditions brought about by the sound 
films. This new model is for use in the 
theatre or exchange. 

The use of this machine which is really 
an instrument of precision, though simple 
and dependable, will, it is stated, accom- 
plish many very desirable results some of 
which are mentioned below : 

The machine itself cannot injure or 
scratch the film. It has no sprockets, and 
from the time the film leaves the upper 
reel until it is rewound on the lower reel 
nothing touches the picture surface or the 
sound track. 

The film is inspected as it is rewound 
and is kept in good condition, safe for pro- 
jection, by discovering and pointing out to 
the projectionist or film inspector all bad 
spots which should be repaired. 

It detects and stops the film at the small 
as well as large tears, or breaks, both in- 
side and outside or between the sprocket 
holes and open splices, or splices that are 
badly made and apt to open, or are just 
starting to open. 

If it is desired, the machine can be set 
to stop at each splice in the film so they 
can all be closely examined. 

The film inspection machine prevents 
tiny breaks and tears from becoming large 
ones by assuring their discovery and re- 
pair before they become enlarged and dan- 
gerous through repeated projection. Thus 
repairs to synchronous or silent films can 
be made and only one or two frames re- 
moved and replaced with black leader or 
not as the type of film may require. It 
is bad in all cases to have to take out 
rather long pieces of the film. With 
synchronous films it is sometimes dis- 

The rewind from the beginning to the 
end of the reel is even and solid without 
pulling too hard on the film. In fact no 
harm can come to the film from the pull 
of the take-up because there are no 
sprockets or sprocket teeth for the take- 
up to pull against. 


The new film inspecting machine. 
The indications show: 1, 17-inch 
magazine; 2, detector box; 3, detec- 
tor box gate; 4, fire valve through 
which the film is threaded; 5, film 
chute through which the film is 
automatically threaded; 6, table 
top; 7, starting handle; S, casting 
housing the mechanism; 9, casting 
housing the motor; 10, electric cable 
and plug. 


The Radio Receptor Company of 106 
Seventh Avenue, New York City, has just 
introduced a new microphone amplifier for 
portable or stationary use in public address 
and similar systems. This amplifier is being 
produced in two types, namely, one for a-c. 
operation, and the other for battery opera- 
tion. The battery type employs two tubes, 
and has an output of approximately .35 
watt. The a-c. amplifier employs two -27 
tubes and an -80 rectifier, with an output 
of approximately .45 watt. The amplifier 
is built as a single, independent unit, but is 
so constructed as to permit of rack mount- 
ing, if so desired. 

Projection Engineering, October, 1020 

Page J t 5 




MANY times, a suggestion 
from the outside — an un- 
biased opinion — saves needless 
loss of time and money. 

The complete resources, the 
combined experience of the en- 
gineers of the Perryman labora- 
tories are available to help you 
solve your vacuum tube prob- 
lems. This group developed 
and perfected the famous Pat- 
ented Perryman Bridge and 
Tension-Spring now incorpo- 
rated in Perryman Radio Tubes. 

Submit your problem in writing, 
giving complete details. Your letter 
will receive our immediate attention. 
The recommendation of our labora- 
tories will be forwarded to you 
within one week. 


Laboratories b^H and Plant 

Hudson Boulevard, North Bergen, N. J. 

The Tube 
with the 


Acme Wire Products 

Parvolt Filter and By-Pass Condensers 
Coils — Magnet Wire "Wound 

Varnished Insulations 
Magnet Wire — All Insulations 

• All products made to Recognized Com- 
mercial Standards, including those of: 
National Electric Mfrs. Assn. 
Radio Manufacturers Assn. 
American Society for Testing Materials 

For 25 years manufacturers and sup- 
pliers to the largest and most discrim- 
inating users. 

The Acme Wire Co. 


New York 
52 Vanderbilt Ave. 

Branch Offices 

842 N. Michigan Ave. 

Guardian Bldg. 

1{ola Model 

HPODAY the demand is for greater reliability — 
■*• more consistently fine performance — from radio 
sets. Dealers are becoming particularly careful as to 
the loud-speakers installed in their merchandise. They 
realize that the loudspeaker is the heart of the radio 
set — that it is the speaker that tells the story. 
Radio engineers find Rola electro-dynamics brilliant 
in performance — rugged and dependable under the 
most exacting conditions. Even more important : they 
know the fine tone quality and range — shown in 
their laboratory tests — will be uniform with every 
Rola speaker installed. 

Rola reproducers meet the modern demand for con- 
sistent high-quality performance. They serve users 
faithfully. They help convince the dealer of the 
merits of the set as a whole. They loyally support 
the recommendations of the engineer. They reflect 
most favorably upon the reputation of the set 

There are Rola electro-dynamics for installation in 
receiving sets, electric phonographs, talking pictures, 
auditoriums, schools, and public address systems — 
wherever reliability and quality are desired in the 
re-creation of sound. Inquiries for details, blue- 
prints and prices from responsible 
' IL, r manufacturers are solicited. 

2570 E. Superior Avenue 

Forty-fifth and Hollis Streets 

Page J,6 

Projection Engineering, October, 1929 


A projector shutter designed to open and 
close toward the center from three sides, 
thereby eliminating any drag of light, and 
which it is claimed passes 50 per cent more 
light to the screen than the standard type, 
has been brought on the market by the 
Globe Reliance Corporation, 29 Glenwood 
Avenue, Minneapolis, Minn. 

The device is called the Berger Shutter, 
which operates on new principles. 

Features of special note incorporated in 
the Berger Stutter are that a clearer 
picture is given, because the shutter runs 
over the 60-cyele. Increased screen bright- 
ness with present light or equal bright- 
ness with reduced light intensity are 

Each frame is on the screen a trifle 
longer through the action of the shutter, 
and thus the spectator catches a clearer 
and more distinct picture. Subtitle tails 
are cleared up, because the shutter opens 
and closes from and toward the center 
from three sides. The shutter allows a 
75 or thereabouts revolution and gives back 
the picture as taken by the camera. 


Mechanical design that makes use of 
"natural forces — gravity, inertia, momentum 
— in preference to complicated mechanisms" 
to overcome common difficulties encountered 
in talking picture installations, it is claimed 
by A. Des Biens, president of Simplimus, 
Inc., of Boston, Mass., and designer of the 
Simplimus synchronous disc reproducer, is 
the principle upon which he has produced 
a machine that is simple in construction 
and makes for the greatest simplicity of 



The Simplimus turntable, pickup 
and coupling mechanism. 

"Among the most common difficulties that 
it is most desirable to overcome in talking 
picture reproducer design," Mr. Des Biens 
says, "are the following : 

"1. Most projection booths are shaky, due 
to vibrations from motors, generators, etc. 
This difficulty has been overcome by putting 
a lot of weight in Simplimus equipment. 
Weight is the enemy of vibration. 

"2. Most projectors have considerable 
gear back lash, causing flutter in the tone. 
This we correct by momentum, the turn- 
table is not only heavy but the weight is 
at the outside, on the flywheel principle. 

"3. Reproducers that render musical 
sounds with good tonal quality often pro- 
duce muffled qualities in human voice 

reproduction. Clear diction is the result of 
distinct rendition of the consonants, or lip 
sounds, like 's' and 'th', which are in 
the region of high frequencies. Here is a 
problem to be taken care of by good 
engineering practice in the design of the 
electrical end of the system. Simplimus 
uses the Audak pickup, which renders the 
high frequencies, in connection with a fader 
of correct impedance to match the pickup 
to the input of a Pam 19 Samson, six tube 
amplifier, which in turn is designed to 
work into the input of a bank of Wright 
Be Coster dynamic speakers, used in the 
Simplimus system." 


The Royal Amplitone sound reproducer is 
one of the first systems to be brought on 
the market to supply the demand for 
synchronized reproducers. Originally it was 
a single-system disc reproducer, but this 
year the sound-on-film reproducer head was 
developed by the company's engineers, under 
Rudolph Miehling, engineer who specialized 
in theatre work before his entry into the 
held of sound reproducer design and con- 

The Royal Amplitone main amplifiers 
operate from current, eliminating all 
batteries. There are two tvpes or models 
the 20-S the larger is designed for theatres 
up to a capacity of 4,000 seats, while the 
smaller unit, the 12-S is for auditoriums 
with a capacity up to approximately 1,000. 
Both have amplifiers that are of the 110- 
volt, a-c. type, and use standard com- 
mercial vacuum tubes throughout 

The film reproducer has been developed 
tor Simplex projectors. The sound head is 
attached to the bottom of the projector 
head mounting place by bolts. The lower 
magazine is dropped only about two inches, 
which allows ample space for convenient 
threading. When silent or disc pictures are 
projected, the film does not thread through 
the film sound attachment, but is threaded 
directly into the lower magazine. When 
film recordings are used, the film leaves 
the last sprocket in the projector head and 
passes over an idler under spring tension 
a feature exclusive with the Roval Ampli- 
tone, device, and designed as a' means to 
minimize flutter. At that point the film is 
intercepted and aligned by a guide roller 
and then enters the sound gate. It is then 
pulled through the sound gate and aligned 
by means of a sprocket driven from the 
main projector drive shaft, then passing 
over another idler into the lower magazine 

The optical system is adjusted at the time 
of installation and locked into the gate 
assembly. The assembly may be removed at 
any time to clean the lens without disturb- 
ing adjustments of the optical system The 
exciting lamp adjustments are' controlled 
by means of thumbscrew adjustments The 
photoelectric cell is located at the ton of 
the sound head and the voltages as received 
from the cell pass into the film amplifier 
located on the front wall of the booth 

Gears in the Simplimus coupling 


High reflective quality without sacrifice 
of sound porosity of screens designed 
especially to meet the requirements of talk- 
ing pictures, is claimed for a new type of 
material developed by the Beaded Screen 
Corporation. 448 West 37th St., New York 
City, and called Vocallte. 

The Vocalite material is the result of 
extensive experimentation directed toward 
the development of a reflective surface that 
would give the greatest light value while 
providing for extreme sound permeability. 
It is manufactured by a new process that 
applies glass beads of the smallest size 
obtainable from foreign glass makers — the 
beads are no larger than grains of fine 
beach sand — to a silk fabric of coarselv 
woven texture providing for porositv to 
sound. The glass beads form a coating' over 
the threads that produces a glistening sur- 
face, having high reflective qualities, but 
leaving a large quantity of openings, irreg- 
ularly scattered, between the threads. The 
screen is a cream white color and projects 
a soft pure white. 

The manufacturers claim that Vocalite 
will give one-third more light and from five 
to six times more sound permeability. The 
material is fire proof, and is easily cleaned. 
Owing to the highly polished surface given 
the threads by the bead coating, dust will 
not adhere to the material. The process 
used in applying the beads makes them 
adhere permanently to the silk fabric base, 
and permits rolling the material without 
damage to the surface, the character of 
which is such that the light projected 
thereon will not refract. 

The Vocalite sound screen may be 
cleaned by scrubbing with soap and water 
or going over the surface with a vacuum 
cleaner. The principles involved in the 
making of the screen are an entirely new 
development in the use of glass beads for 
this type of material construction. 


The National Carbon Company, New York 
City, are marketing the first commercially 
developed neon tube for television receivers, 
known as the Eveready Raytheon Kino 

The Kino Lamp provides a uniform glow 
over the entire plate area without the use 
of mirrors of ground glass. 

The Kino Lamp can also be used in a 
neon stroboscope, for the study of mechan- 
ical movement and so on. 



Eveready Raytheon Kino Lamp. 




A new model called the Super-Mellaphone 
reproducer, was recently launched on the 
market by the Mellaphone Corporation, 
Rochester, N. Y. 

The machine incorporates features de- 
signed to prevent flutter or sound vibra- 
tions, which are described as follows : 

"First, the Mellaphone equalizer-filter, 
consisting of a series of well-constructed 
springs and second, two balanced flywheels 
and specially cut gears, are new develop- 
ments which enable the machine to with- 
stand vibration and prevent effects of them 
reaching into the sound reproducer. 

"The new machine has a new style tone 
arm and pickup which insures perfect 
tracking for all records. Connection with 
the projector is made to the main drive 
shaft. Ball bearings are used throughout." 

Projection Engineering, October, 1929 

Page J,7 

The Burt Reproducer for Talking Motion Pictures 

Burt Reproducer on Poicers Projector 


Synchronous Motor Drive (110 or 220 volts, 50 
or 60 cycles). Prevents variation in speed 
from variation in line voltage, or projection 

The Super Cells used require only two stages in 
head amplifier, hence less distortion. 

Ease op Threading. When running disk or silent, 
the Sound-on-Film unit is not threaded. Sound- 
on-Film threads as easily as through a Powers 

Turn Table Is Accessible, being up high at the 
side of the machine. 

Easy to Install. Installation can be made by 
the ordinary operator, and wire man. 

Projector Head is driven by its main drive gear 
and is not required to drive any part of the 
sound equipment. 

Only Three Shafts : (1) Motor Drive Shaft, 
(2) Sound Film Shaft, (3) Disk Table Shaft. 

Variable Speed can be used for making schedule 
by driving the head off the Powers Motor, when 
running silent. Change from synchronous drive 
to variable speed drive requires about ten 

No Universals — No flexible couplings, flexible 
shafts, or long unsupported shafts are used, as 
these produce tremolo. 

Fire Hazard Is Decreased by use of this equip- 
ment. Failure of take-up does not cause film 
to pile up in light. 

Write for Bulletin No. 291 

Manufactured by 



900-904 East California St., 

Pasadena, Calif. 

Specialists in 




Write Our Engineering Department 


335 West Madison St., 
Chicago, 111. 

Dependability to 
the great new industry of Sound Projection. 

For Amplifiers: — Polymet high-wattage resistors 
Poly met high-voltage filter condensers. 

For Equalizer Networks: — Polyniet small fixed con- 
densers — Polymet resistors. 

For Power Transformers, Audio Frequency Trans- 
formers, Impedance- Adjusting Transformers, Loud- 
speaker Units: — Polymet Coils ("Polycoils") 

2Bk Send lor our catalogue giving complete specifi- 

m ^^, TOW cations of Polymet Products. 

JEHBugS We will gladly supply samples and work with 

W SjflLjtet y° u to meet particular specifications. 

^jpj Polymet Mfg. Corp. 
I 839-A East 1 34th St. 

•^p New York City 

Polymet Products 

Page J t 8 

Projection Engineering, October, 1929 


by the fore- 
most electri- 
cal and radio 

5 TO 5,000.000 OHMS 

The first 
p tactical 
wire -wound 
high - resist- 
ance unit. 

Practically negligible inductance Minimum distributed capacity 

Tolerance of accuracy ± 1 % Closer tolerance if specified 

Temperature coefficient, .0001 Safe load 1 watt 

Size 2" long, V%" diameter 

THE DAVEN COMPANY, 156 Summit St., Newark, N. J. 

^i' ■ 'in , u; ; jj ;;- 1:;; ■ ; ;;; . ' . ;;; ' ■ . I'j, -'r M, : . -'|i| -!.;: ^11:: r'l. : ^ . |M I :i i.-lllll/'l'!!.:- 1 !!!. i 1 ;'.-!- ''Hirni,!!.^ 





FOR YEARS the name of CROWE has 
been synonymous with fine escutcheons 
and name plates, and the demand for 
CROWE products in the radio, phono- 
graph, and electrical fields attests to this 

WE ARE prepared to submit to manu- 
facturers in the sound and light projec- 
tion industry samples and estimates on 
name plates, segments, dials, scales, spe- 
cial embossings and escutcheons. 

CROWE ENGINEERS will give careful 
personal attention to each manufacturer's 
problems, and invite consultation — with 
tio obligation on your part. 

"Travel by Air - - - Use Air Mail" 
Crowe Name Plate 8 manufacturing company 

175 6 Grace St., Chicago, 111. 

Chicago: Fred earner Co., 


All Kinds from $10 to $300 

For Public Address, etc., list $25 

Standard Broadcast Model, list $75 

Condenser Models for Film and Record Work, 

list $250.00, $300.00 

Also Desk and Floor Stands, Covers, Cords, etc. 


Inglewood, Calif. 
9 S. Clinton St. New York: Gotham Eng. & Sales 

Co., 130 W. 42nd St. San Francisco: C. C. Langevin Co.. 274 Brannon St. 

Special Frames and Horn Towers made to ^ 

order. Talking 

Picture Equipment a 


,, Bakelita and Hard Rubber Panels ma- 

i chined and engraved to your specification. 

Aluminum cans and boxes made to meet 

any requirement. 

All kinds of special experimental work, 
models, etc. Our A-l reputation, backed 
by 12 years of experience is your guarantee 
of complete satisfaction.' Send us your Blue 
Prints for quotation. 


Television Scanning Discs 

Standard 12" Aluminum Disc with mounting for W shaft either 24, 
48, 60 holes on spiral each, $8.00. Steel Bushing for mounting on %" 
Bhaft each, 75c. G-10 Neon Lamp for Synchronizing Motor speed, 75c. 
These Discs are now being used hy leading Television Developing Engineers. 
Special Discs made to your specifications. Standard Neon Lamp plate 
size Wz" x l 1 /^" stands steady load of 50 milliamperes each, $8.00. 

3541 Michigan Ave., Detroit, Mich. 


Send sketch or model for examination and advice. No charge for 
preliminary advice on patents, trade-marks and coyprights. Moderate 
fees. Careful personal service. 


Registered Patent Lawyer, 
70 Washington Loan and Trust Bldg., Washington, D. C. 

PHOTO CELLS, neon lamps, special high 
vacuum or gas filled tubes, and noise-free 
liquid grid leaks, manufactured to specifications. 

150 West 22nd St. New York City 

AEROVOX or DUBILIER — "High Voltage" 

7-Mfd. Filter Condensers — Containing as follows: 
2-Mfd. 1000 D. C. Working Voltage 
I- " 800 " 
1- " 800 " 

3- " 400 " " " $2.50 ea. 

Filter Condenser 2-Mfd. R.C.A. 250 Working Voltage .35 ea. 
Filter Condenser 3y 2 -Mfd. Stromberg 600 Working 

Voltage $1.50 ea. 

Weston Voltmeter; Model 506 — 0-7. List $7.00 $1.65 

Filter Condenser 7-Mfd. Dubilier 600 Working Voltage.$2.50 ea. 

Filter Condenser 
Filter Condenser 
Filter Condenser 
Filter Condenser 
By-Pass Condenser 
By-Pass Condenser 

1-Mfd. Splitdorf 





600 D.C. 
Grebe 3 00 

Polymet 300 
Stromberg 25 

Volts . .60 

" . .35 

" . .15 

" '. 2.75 

Dubilier Type 907 . .32 

Dubilier " 907 25 

F.O.B. Our New York Warehouse W. K. SKIDMORE & CO., WoolvVOrth Bldg., N. Y. C. Other Specials Available 

Projection Engineering, October, 1929 

Page 49 

Jenkins 8C Adair Condenser Transmitter 


The type C condenser transmitter is the result of two years actual 
experience, during which these instruments have been used under all 
conceivable conditions, and in practically every part of the world where 
broadcasting or electrical recording is carried on. In addition to their 
excellence as pickup devices, they have proven to be extremely durable 
and rugged, and have shown a minimum upkeep cost. 

The type C transmitter is built for 6 or 12 v. A battery, and 180 v. 
B battery. The filament draws ^4 amp., and the plate, 3 to G M. A. 
The amplifier has a single stage and uses a standard tube. The trans- 
mitter unit is heavily gold plated, and the case is finished in dark 
brown enamel. 20 ft. of special double shielded cable with plug and 
socket are supplied. Our bulletin No. 6 describes this instrument in 

3333 Belmont Ave., Chicago, U. S. A. 

Cable Address : 

Keystone 3 18 

Makes "Silent Drama" Theaters 

Acoustically Perfect 

at Low Cost 

So amazing are the results 
achieved by this material . . . 
and so economical is it to install 
. . . that over 600 exhibitors 
have recently placed it in service. 
You should have all the facts 
about Acoustical Westfelt now. 

Send for this FREE Book 
Every exhibitor should read this 
book on Acoustics. Gives you 
the causes of poor acoustics and 
the remedy . . . tells you how to 
get desired results at lowest 
cost. Send for your free copy 
of this book today ... it has 
saved thousands of dollars for 
theater owners, everywhere. 

Acoustical Westfelt 
is furnished in flame- 
proof finish. It is 
available only in rolls 
Va" and 14" thick, 54" 
wide and 75" long. 
Price per square yard, 
54" thickness, 45c — 
y 2 " thickness, 75c. 

Acoustical Division 


4029-4115 Ogden Avenue Chicago, Illinois 

Also Manufacturers of Rug and Carpet Cushions and 
Manufacturers and Cutters of Felt for all uses 

/^ — at i 

Undistorted Power 
we, Mellow Tone 
a moderate price 






The thin, high note of the piccolo, 
the sonorous low "E" of the bass 
viol — Amplisound reproduces them, 
and every sound in the audible 
range, with striking fidelity. 

This is because Amplisound Sys- 
tems are built for pure tone, and 
no factor however small is slighted. 
Amplisound employs a 3-stage 
audio system, with exclusive de- 
signs in transformers, filters and 
speakers. Additional stages may be 
coupled for any extra power 

Amplisound Systems are complete 
for reproducing voice or orchestra, 
radio programs, synchronized talk- 
ing picture discs, or standard 
phonograph records. 
Amplisound engineers offer free 
consultation service on all problems 
relating to sound amplification or 
•^•jT*'©^^, reproduction. Amplisound Systems 

*^ .i»>.. cilrl nnrl in e1 :i I l.»rl nnilpr mir 

BoU' 00,ns 




are sold and installed under our 
own supervision, also leased tem- 
porarily. Write for full informa- 




224 North Desplaines St., 
Chicago, Illinois 

Page 50 

Projection Engineering, Octooer, 1929 

General Industries Corporation 

Manufacturers of 

Radio Broadcast Equipment 

222 Grove Street, Waltham, Mass. 



Two Button Microphones 

Condenser Microphones 

Microphone Stands, 

Springs and Cords 


Repeater Racks 

Panel Equipment 

The General Industries Microphone is of the 
standard two-button, stretched diaphram, 
carbon granule type. It has an impedance 
of about two hundred ohms, and is de- 
signed to work into the standard micro- 
phone input transformer. The frequency 
response characteristic is uniformly flat 
from 30 cycles to 7000 cycles per second, 
thus giving faithful reproductions on all 
voice and musical frequencies. 

Due to the careful selection of the carbon 
grains, the level of the "carbon hiss" is low 
as compared to other makes, thus making 
it especially adaptable to organ reproduc- 
tion and recording work. 

JANETTE Motor-Driven 
Speed Reducers 

Quiet, smooth-running machines consisting of motor 
and worm-gear reducer in one compact unit. Motor- 
end frame is cast integral 
with the gear housing, a 
unique construction conducive 
to compactness and perfect 
shaft alignments. Reductions of 
20 to 1 to 50 to 1. Motor speeds 
1750 or 1150. Sizes 1/30 to 
1/3 H.P. 

Write for 
Bulletin SR-529 



Transforms DC 
to AC to operate 
AC radios, elec- 
tric talking ma- 
chines, public 
address systems 
and motion pic- 
ture sound equip- 
ment in DC dis- 

Janette Mfg. Company, 

Singer Bldg. 
149 Broadway 
New York 

561 W. Monroe St., 

Real Estate 
Trust Bldg. 

specially design- 
ed for talking 
motion picture 
machines. Motor 
speed 1750 RPM; 
turntable speed 
33% EPM. 








t 1802 




with the ma- 

jority of 

of Sound on Film 

ere's A Reason 


Grace St. 

Chicago, 111. 




AC Operated Speech 

Public Address. 

Mixing Panels. 

Power Supply Panels and 

Recording Amplifiers. 

55 East Wacker Drive, Chicago. 


Allied Die-Casting Corp 9 

American Transformer Co. .Third Cover 

Amplisound Systems, Inc 49 

Amrad Corp., The 5 

Arcgo Laboratories, Inc 48 

Rest Manufacturing Co 

Burt Scientific Labs, Robert C . 

Cameron Publishing Company. 

Clarostat Mfg. Co 

Crowe Name Plate & Mfg. Co. 

Daven Radio Corp. 







Electro-Acoustic Products Co 50 

Elkon, Inc 6 

Enterprise Optical Company 

Back Cover 

Ettco Tool Co., Inc 11 

Ettinger Security Construction Corp. 10 


G-M Laboratories, Inc 50 

General Amplifier Co 52 

General Industries Corp 50 

Gilby Wire Co 3 

Janette Mfg. Co 50 

Jenkins & Adair, Inc 49 

Lynch Mfg. Co., Inc. 


Pohl, Arthur M 48 

Polymct Mfg. Corp 47 

Projectionist Sound Institute 51 

Republic Metals Co 12 

Ruden & Aaaras 10 

Samson Electric Co Second Cover 

Shure Brothers Co 47 

S'kidmore Co.. W. K 48 

Stevens, Eugene E 48 


United Radio Mfg. Co 48 

Universal Microphone Co 48 


Ward Leonard Elec. Co. 
Western Felt Co 


Zapon Co., The 14 

Projection Engineering, October, 1929 

Page 51 


Was Created in Response to a Pressing 

Demand for a Correspondence School 

of Electrical Acoustics by Those Who 

Are Now Identified with the Art of Talking and Sound Pictures — Also for the 

Thousands That Will Have to be Drawn in to Meet the Ever-Increasing Demand 

for Sound Engineers. 


Our guarantee insures you 
that if you enroll as one of 
our students and take advan- 
tage of the many opportuni- 
ties to which your member- 
ship entitles you, your in- 
creased income will pay the 
tuition of the course many 
times. We unconditionally 
guarantee that if for any rea- 
son you are dissatisfied (you 
being the judge) we will re- 
fund every cent you have 


Our course on Sound Projection, 
which is prepared by the most 
eminent authorities on electrical 
acoustics, will qualify you for a 
profession whose place in the en- 
gineering world is second to none. 
All the available knowledge of 
the art and the underlying funda- 
mental principles of Sound is given 
to you in an every-day, plain-talk 
language, as well as two weeks 
practical training in the operation, 
servicing and installation of Sound 


In the 20,000 theatres throughout the 
United States and Canada, which now 
employ approximately 50,000 projec- 
tionists, it is estimated that a very small 
per cent of this number are qualified 
to fill the position as Sound operators. 
Many thousands of new men will have 
to be taken into this field as fast as the 
many unwired theatres are wired for 
sound as the additions of sound doubles 
the number of operators required. This 
condition will create many thousands of 
positions at salaries ranging from 
$75.00 to $200.00 per week. 

The tuition for these courses is very reasonable and is payable in easy installments as you 
study. Also you have the added convenience of studying at home in your spare time. Fill out 
and mail the coupon below today for special scholarship proposition. 


F. A. JEWELL, Gen. Mgr. 

P. O. Box No. 28 Easton, Pa. 


P. O. BOX No. 28, EASTON, PA. P. E. 10 


Please send me by return mail full details of your special 
Scholarship Proposition on Sound Projection. 



City State. 

Page 52 

Projection Engineering, Octooer, 1929 

S 0SN 



is the manner in which many critics have 
expressed themselves after enjoying a sound 
demonstration with GENERAL AMPLI- 
FIERS and we believe this fittingly describes 
our devices. 

You will undoubtedly have to supply much 
sound apparatus and if your first installation 
meets with complete satisfaction you are in 
line for some interesting business. The am- 
plifier is the nucleus of all sound installations, 
so why not be safe with a GENERAL 
AMPLIFIER? We offer a laboratory-tested 
device and one guaranteed against defects 
in workmanship. All GENERAL AMPLI- 
FIERS possess unusually flat frequency char- 
acteristics and provide for the full undis- 
torted power output of the tubes employed. 

We maintain a free engineering service and 
are desirous of co-operating at all times. 
Consult us freely and write for Bulletin 
PE-1 today. 

Model GA-20 (Less Tubes) $225.00 


27 Commercial Aye. 
Cambridge, Mass. 

565 Washington Blvd. 274 Brannan St. 

Chicago, 111. San Francisco, Cal. 


guaranteed f 

With our greatly increased manufacturing facilities 
at Maiden, Mass., and at Cranford,, N. J., we abso- 
lutely guarantee prompt delivery of Resistors for 
EVERY Resistance Need for at least the next eight 
months, no matter how large or how small the order. 
Our factory facilities and our complete line of qual- 
ity resistances will enable us to satisfactorily take 
care of your requirements. We can give you WHAT 
you want, WHEN you want it. 


Veritas Resistors 

are supplied in either cartridge or pigtail 
type, and are made in four sizes with 2 
watt, 5 watt and 1 watt ratings. Capacities 
range from 500 ohms to 10 megohms. The 
Lynch Veritas Resistors have the metallic 
resistive coating fused to the inside of the 
glass, and can run a great heat without 
change in value. Not affected by humidity 
— non-absorbent. It is as perfect a resist- 
ance as can be made. 


Dynohmic Resistors 

Furnished in cartridge or pigtail type, capa- 
cities ranging from 250 ohms to 10 meg- 
ohms, '/2, 1 and 2 watt types. The resist- 
ance element is based on the famous metal- 
lized principle which has proved its supe- 
riority where accuracy and uniformity are 
of paramount importance. 

Special sizes of ALL Lynch Resistors can be made to 
order on very short notice. 

Lynch Resistors are specially suited to the exacting needs 
of manufacturers of sound and light projection equipment 
■ — theatrical and home talking movies — home entertain- 
ment equipment — cameras, recording and amplifying 
devices — television, etc. 

Approved by leading engineers. 

Endorsed by test and experimental laboratories. 

Employed by scientific apparatus and 
precision instrument makers. 

Selected by discriminating radio receiver manu- 

Send us your specifications. Get our prices. Let us 
send you samples. Be prepared for any emergency 
that may confront you. Descriptive folder upon 

Lynch Manufacturing Company, Inc. 

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Television - Sound and Light Projection - Theatrical Engineering 



Vol. I 

OCT 6 1930 





No. 3 



6 & 




(Page Eleven) 
By William H. Bristol 


(Page Twelve) 
By Haviland Wessells 


(Page Fourteen) 


(Page Twenty-Two) 
By J. Garrick Eisenberg 


(Page Sixteen) 
By E. W. D'Arcy 


(Page Twenty) 




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Projection Engineering, November, 1929 

Page 1 

These photographs from the film "On 
With The Show" were furnished by 
the Warner Brothers theater, Holly- 
wood, California. Like all the Warner 
Brothers studios, the stage of this 
theater is lined entirely with Gimco 
Rock Wool Flexfelt sound insulation. 

Every voice 

in its clear 

natural tone 

A Marvel in Sound Reproduction 

"On With The Show," a Vitaphone Production staged in the new 

Warner Brothers studio, Hollywood, California, is an outstanding 


The ideal acoustic conditions established by the exclusion of outside 

noises and absorption of disturbing sounds by lining the entire interior 

walls and ceilings with a layer of GIMCO 


Sound Insulation 

played an important part in obtaining almost perfect tone reproduction 
on this full color film. 

"Gimco" Rock Wool Flexfelt Sound Insulation has the most uniform 
sound absorption coefficient at all vibrations from the lowest to highest 
pitch. It is also 100 per cent fire-proof, being made from pure silica 
fibre covered with fire-proof muslin and strongly reinforced with metal 
screening. It is furnished in convenient slabs measuring 2 ft. x 8 ft. 
or 4 ft. x 8 ft. of the thickness recommended by our engineering depart- 
ment for each specific application. The slabs are mechanically strong 
and flexible for mounting on flat, curved or irregular surfaces. 

Nearly 2,000,000 square feet have been sold for sound proofing, auditoriums, theaters, 
hospitals, apartment houses, laboratories, and other buildings. 
Consult us on your specific problem. Write for bulletin. 

R. P. CARMIEN, Los Angeles, Calif. C. W. POE COMPANY, Cleveland, 0. 
H. M. GASSMAN, Birmingham. Ala. . L, MUNDET & SONS, St. Louis, Mo. 
E. T. KELLEY, Houston, Texas SEATTLE ASBESTOS COMPANY, Seattle, Wash. 
^^ _^^_^^^_^_^^^^__ N. MET1TON. Detroit, Michi gan .IQNES BROS.. S AM FRANCISCO. Calif. 

GENERAL INSULATING 8C MFG. CO., Alexandria, Indiana 



Western Editor 

Evans E. Plummer 

Advisory Editor 

Donald McNicol 

M. L. Muhleman 

Associate Editors 

James R. Cameron 

Austin C. Lescarboura 

John F. Rider 

Vol. 1 

November, 1929 

Number 3 


A New Synchronized Apparatus for 16 mm. Films With Disc Records By William H. Bristol 11 

Sound — ■ as the Customers Hear It By Haviland Wessells 12 

New Theatre Light Control System 14 

Public- Address and Centralized Radio Systems By E. W. D'Arcy 16 

Recording on a Steel Wire 19 

' ' Narrowcasting ' ' with the Photophone 20 

Notable Advances in the Motion Picture Industry By J. I. Crabtree 21 

Testing Characteristics of Loudspeakers 21 

Mechanics of the Talking Movies By J. Garriek Eisenberg 22 

The S.M.P.E. Toronto Convention By P. A. McGuire 25 

Considerations in the Design of Audio-Frequency Apparatus, Part II By C. H. W. Nason 26 

A Few Facts About Filters By John F. Rider, Associate Editor 29 

The Portable Model RCA Photophone By II. L. Danson 32 

Standardized Sound Film Aperture Recommended 34 

The Photoelectric Cell 35 

D epartm ent s 

News of the Industry 36 

New Developments 40 

Index of Advertisers 46 

Aviation Engineering 
Radio Engineering 
Projection Engineering 

Published Monthly by 

Bryan Davis Publishing Co., Inc. 

Publication Office — Lyon Block — Albany, N. Y. 

Chicago Office — 333 No. Michigan Ave., 
Cleveland Office— 10.515 Wilbur Ave., 
San Francisco Office— 318 Kohl Bldg. 
Los Angeles Office — 846 So. Broadway 

Charles Farrell, Mgr. 
James Munn, Mgr. 

Cupit and Birch 

Bryan S. Davis, 


James A. Walker, 


G. C. B. Rowe, 

Advertising Manager 

Application for entry as second class mail matter 
at the Post Office, Albany, N. Y., pending. 

52 Vanderbilt Ave. 
New York City 

Yearly subscription rate $2.00 in U. S. and 
Canada; $3.00 in foreign countries. 

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Projection Engineering, November, 1929 

Page 3 

^JHak the, SOUND as (jood 'as tkP/C7ll/?cL 

Dorothy Mackaill 

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might be as good as the Picture . . . has been realized. 

Just as talking pictures developed wholly new standards of entertainment so have 
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The Ferranti Standard is fixed. It can be achieved by adapting Ferranti Audio 
Transformers, Ferranti Chokes, Ferranti Input Transformers, Ferranti Output 
Transformers . . . whichever may be needed ... to the requirements of the 

Put your sound reproduction problem on a new installation or a faulty old 
one up to Ferranti engineers. They will weigh the variable factors and 
recommend equipment to give you the splendid undistorted, natural 
sound reproduction which only Ferranti has achieved . . the perfect sound 
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New York, N. Y. 



Page 4 

Projection Engineering, November, 1929 





November , 1929 

I. A. T. S. E.—M. P. M. O. U. 

THE purposes and policies of PROJEC- 
TION ENGINEERING have been out- 
lined once before. The outline, how- 
ever, was general in character and 
we wish, at this time, to further amplify the 
aim of this publication in its relation to the 
vast legion of workers in the theatres. 

The fact that the word "engineering" is a 
part of the name of this publication has, in 
some instances, given a wrong impression of 
the field we cover. The word "engineering" 
is utilized because the greater percentage of 
material printed is of a technical nature, but 
it does not, by any means, imply that these 
technical articles are all profound and under- 
standable only to the man who does his work 
with a "slip-stick." Nor, that we, as pub- 
lishers of a technical medium are serving 
only an engineering group. 

It takes over 3,000 amperes to start the 
average electric train but once the motors 
have conquered the potential inertia, the train 
consumes little more than 700 amperes. We 
have been consuming a lot of "juice" over- 
coming the inertia of this publication, now in 
its third issue. It not only takes "juice" but 
a bit of time to get a new publication into its 
stride ... to step gingerly along new and 
forgotten roads ... to walk blindly some- 
times, until we reach a bit of light . . . 
always feeling our way until we know the 
good roads and the bad ones. 

In the study of the sound and light projec- 
tion fields, before the institution of this pub- 
lication, we were unable to locate any true 
medium of valuable information for theatre 
and stage employees, and projectionists — the 
publications in existence appeared to be 
devoted to other causes than that of dis- 
seminating educational material. Therefore, 
it became one of our greatest aims to func- 
tion as a source of authentic technical in- 
formation for the members of the I. A. T. S. E. 
and the M. P. M. O. U. . . . that they might 

know of every new development in a fast- 
moving field . . . that they might, through 
this medium, learn every technical angle of 
the industry, from studio recording through 
to the final elements of sound projection. 
Along with this, is a sincere desire to co- 
operate in any way possible with the 
I.A.T. S.E. and the M.P.M.O.U. that we 
may, to the best of our ability, assist in solv- 
ing the technical problems of the field, both 
individually and collectively . . . and, at the 
same time, attempt to overcome some of the 
existing inertia in connection with the matter 
of the distribution of the existing knowledge 
of recording and projection technique and 

We have since learned that the producers 
are very anxious that the "men in the field" 
know more of what they are doing, of what 
their problems are . . . and also anxious 
themselves to learn more of the technical 
problems in the theatres. That it is very 
difficult for the two groups to get together is 
evident, particularly when there has been no 
satisfactory medium through which views 
can be made common. 

The present issue contains a number of 
articles dealing with the technique of record- 
ing and projection and the attendant prob- 
lems. Two articles in particular are directed 
to the projectionists and, we believe, indicate 
that there is not only a strong prevalent desire 
to pass along the inside dope, but likewise, a 
desire to receive, in return, the inside dope 
from the other end of the line. 

In many ways, the problems of the manu- 
facturers and engineers in the factory become 
the problems of the projectionists, managers 
and servicemen in the field. PROJECTION 
ENGINEERING serves both. Suggestions and 
constructive criticism from our readers will 
be welcomed. 

M. L. MUHLEMAN, Editor. 

Projection Engineering, November, 1929 


Page 6 

Projection Engineering, November, 1929 



Since the advent of dry metallic rectifiers Elkon has 
always led in perfection of design and record of per- 
formance. Many of the leading manufacturers have 
brought their rectifier problems to Elkon for solution. 

The signal success of Elkon rectifiers in the "A" Elim- 
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outstanding achievements with low voltage rectifiers 
for dynamic and other moving coil speakers. 

Again, this year, looking ahead and interpreting the 
need, Elkon introduced the new high voltage recti- 
fiers which eliminate the power transformer in 
dynamic speakers and others of moving coil type. 

Whatever may be your problem of rectification, 
Elkon engineers will be glad to co-operate with you 
in working out its solution. 

ELKON, Inc. 

Division of P. R. Aiallory & Co., Inc. 



Projection Engineering, November, 1929 

Page 7 


consult these 

THE manufacturers of DURHAM Metal- 
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Probably the best indication of the value of 
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Page b 

Projection Engineering, November, 1929 

Still the Best Seller in the Industry 

TieBeMitftBe aEeasom 

of these experts 
are equipped with a copy of- 

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Metro-Goldwyn-Mayer believing that nothing short of the 
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ordered a copy of Cameron's new book for each of these 
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The Motion Picture Studios of this country are 1 00% 
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Motion Pictures with Sound 
covers the subject from A to 
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The book measures 7% x 5 

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The book contains complete in- 
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sound picture information. 

Mr. Cameron worked for over 
ten months on this book, and 
has had the active co-opera- 
tion of the technical experts 
of the various Sound Equip- 
ment Manufacturers and 
Sound Picture producers. 


CAMERON PUBLISHING CO., Manhattan Beach, N. Y. 

Projection Engineering, November, 1929 

Page 9 




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Projection Engineering, November, 1929 

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Projection Engineering, November, 1929 

Page 11 

A New Synchronized Apparatus for 1 6 mm. 
Films With Disc Records 1 

Synchronism Gained at Reduced Speed by Reducing Number of 
Frames. Electro-Synchronous Device Employed 

IN the operation of motion-picture 
projectors, where the film is syn- 
chronized with sound recorded on 
a disc or on a film, the standard 
speed of the projector is 90 feet per 
minute or 24 frames per second. 

It will be understood that the sound 
record, whether on a disc or on a film, 
must be reproduced at the same speed 
as it was originally recorded, and in 
order to use the standard theatrical 
synchronized film, whether of original 
width or whether reduced to 16 mm. 
width, it will be necessary to project 
the pictures at this standard speed of 
24 frames per second. 

Professional projectors are always 
operated in booths for fire protection, 
which at the same time prevents the 
audience from being disturbed by the 
noise of the machine. All projectors, 
whether made for 35 mm. or for 16 
mm. films, when operated in the open 
without a booth at the standard 24 
frames per second, make so much noise 
that it is practically impossible to re- 
produce synchronized sound pictures 
satisfactorily. Projectors for amateur 
use are designed primarily to be oper- 
ated at 16 frames per second. At this 
speed, it would usually be impossible 
to synchronize theatrical records, as 
they would only be running at two- 
thirds of the normal speed at which 
they were recorded. 

Reducing Number of Frames 

To overcome the difficulties of oper- 
ating these projectors at the abnor- 
mally high speed that would be neces- 
sary to maintain synchronism and give 
correct reproduction of the sound, we 
have found, by experiment, that we 
can remove every third frame from the 
synchronized film, thus reducing it to 
two-thirds of its original number of 
frames, and when projected at two- 
thirds the speed at which it w y as origin- 
ally recorded, perfect synchronism 

By William H. Bristol* 

will be maintained between the short- 
ened film and the original sound 

Although by this plan, we have 
eliminated every third picture, we 
have found that, due to persistency of 
vision, it does not detract from the 
natural action of the picture. 

By a specially designed printing ma- 
chine, we are able to make prints from 
the original theatrical negatives, 
either of the standard width or the 
16 mm. width, with every third frame 
eliminated. Such prints can then be 
used in either 35 mm. or 16 mm. pro- 
jectors at the reduced speed of 16 
frames per second, still producing 
equally as good results as though the 
pictures had been originally taken at 
16 frames per second. When project- 
ing these films, it is necessary to use 
a shutter designed for the projection 
of 16 pictures per second in order to 
reduce flicker to a minimum. 

Advantages Gained 

The following are some of the ad- 
vantages gained by using this method 
of operating the projectors at the slow 
speed : 

First, it keeps the noise of the pro- 
jectors down to a satisfactory level, 
without using a sound-proof cover, 
thus not interfering with the accom- 
panying sound reproduction ; second, 
it reduces the wear and tear on both 
the projector and films, which means 
longer life for both ; third, by using the 
film of reduced length, there will be 
an appreciable saving in the cost of 
the prints : fourth, this slow speed al- 
lows for increased length of running 

The complete outfit for reproducing 
these special synchronized 16 mm. or 
any other 16 mm. films, consists of a 
turntable unit connected electrically by 
a small cable to the 16 mm. projector, 

Fig. 1. Standard 
16 mm. pro- 
jector with the 
usual motor re- 
placed by a 

t Paper delivered at the Toronto meet- 
ing of the S.M.P.E. 

* ~\\'m. H. Bristol Talking Picture Corpo- 

Page 12 

Projection Engineering, November, 1929 

using the special synchronizers de- 
scribed in a paper presented at the 
meeting of the Society of Motion Pic- 
ture Engineers, September, 1928. 

Special Synchronizer 

We have developed a method of us- 
ing the same type of synchronizing 
motors which were previously de- 
scribed, but now made up into smaller 
models, especially for non-theatrical, 
industrial and educational uses, so 
that the synchronizers can be used to 
replace the motors that are usually 
employed in 16 mm. projectors. For 
illustration, in the 16 mm. Bell & 
Howell projector, we have been able 
to substitute for the motor which is 
usually supplied, one of these syn- 
chronizers as shown in Fig. 1. 

There is no other change in the pro- 
jector, since the gearing at the turn- 
table is made to give the correct speed 
ratios. The cord shown is a cable 
leading to a companion synchronizing 
motor, which is shown at the right- 
hand end of the base of the turntable 
in Fig. 2. 

The electric motor which is shown 
on the left-hand side of the base, 
through a worm and gear located in 
the center of the base, rotates the 
turntable through the vertical shaft 
at 33% revolutions per minute. The 
motor, in addition to driving the turn- 
table, also turns' the rotor of the 
synchronizing motor on the base, which 
generates the current to drive the 
synchronizing motor which has been 
shown as a part of the projector. 

In order to make the synchronizing 
motor small enough to replace the 
original motor in the Bell & Howell 
projector, it is necessary that this 
motor should run at high speed, but 
such a high speed is undesirable at the 
turntable, as it may make noise and 
cause vibration, interfering with the 
perfect reproduction of the sound. 

As we have previously used these 
motors and as described in the previ- 
ous paper referred to, these synchro- 
nizers both run at the same speed, but 
in this case the turntable synchronizer 

Fig. 2. Specially 
designed turn- 
table, with driv- 
ing motor and 
"syn c h ronizer 
generator." for 
16 mm. films. 

i* -—" 






/JL»i* .. 

«—-*«« --m'i \B\ 



J I pUjk 


.."':".' • 

is made to run at one-half the speed 
of that of the synchronizer driving 
the projector. 

Trunnion Bearings Used 

This is accomplished by making a 
four-pole synchronizer at the turntable 
and a two-pole synchronizer for the 
projector. The field of the turntable 
synchronizer is mounted on trunnion 
bearings, so that its field may be 
rotated independently of the rotor. 
The rotation of this field on its trun- 
nion bearings in a direction the same 
as the rotor is turning will cause a 
decrease in the speed of the projector, 
while the rotation of this field in the 
opposite direction to that of the rotor 
will increase the speed of the projector 
without in any way affecting the speed 
of the turntable. 

The handle shown in the illustration 
of Fig. 2 can be used for revolving the 
field of the synchronizing motor in its 
trunnion bearings through a pair of 
gears. By means of this, perfect syn- 
chronism may always be maintained 

without in any way disturbing the 
projection of the picture on the screen. 

It is of the utmost importance that 
the turntable be absolutely free of 
vibration in order to obtain perfect 
reproduction, especially of music. To 
accomplish this, we have developed a 
mechanical filter system which has 
proven very simple and efficient. It 
consists of mounting the turntable as 
shown, on a tripod, which stands on 
the floor independent of the base 
carrying the motors. A vertical shaft 
connecting the motors with the turn- 
table is provided with several flexible 
metal disc joints, designed particularly 
to filter out the vibration that would 
otherwise be transmitted to the turn- 
table from the motor base. 

In addition to the flexible disc, there 
is a double sliding joint which is 
clearly shown in the illustration. This 
double sliding joint, working in con- 
junction with the flexible filter discs, 
has proven to be a most practical way 
of eliminating vibration, which is al- 
ways present at the driving motor. 

Sound — as the Customers Hear It 

The Man in the Seat, His Family, His Friends, Pays the Taxes — Rent — 
Film Rentals — Sound Installation — and Drags the Balance Out of the Red 

IT'S a far cry nowadays back to 
the old times when the lone piano 
player sat in a dark corner and 
ad-libbed Paul Revere's Ride and 
the Burning of Rome during the whole 

I once opened a new house in the 
old days, with piano and drums, and 
we thought we were the berries! All 
the other flickers in town were using 
a piano. 

Then came the transition. The 
chain houses began using small or- 

By Haviland Wessells 

chestras, with organs for relief. The 
Picture Trade Papers published cue 
lists of music suitable for various pic- 
tures, and the musical taste of the 
public began to be cultivated. 

Radio and the Picture 

Several broadcast papers have taken 
the full glory for the uplift of the 
public's enjoyment in better music, 
and given it to radio. 

It does, in a great sense, reflect the 
possibilities of the science, but in a 

greater sense it reflects the slower, 
and possibly more secure foundation 
laid by picture houses that gave a 
thought to good music. 

Which brings us into this present 
momentous and unsettled era. 


With the welding of the phonograph, 
radio and the motion picture, you are 
given a complete and almost perfect 
entertainment. The field of produc- 
tion in this direction has only been 

Projection Engineering, November, 1929 

Page 13 

tapped. The development can be 
safely left to the studios and their 
technicians. The manager's job is to 
reproduce their efforts in a capable 

The Knowing Public 

With the many radio and picture 
papers catering to an interested pub- 
lic, the fundamental principles of 
sound are no longer a secret — if they 
ever were. Sound on film and disc 
have been explained in detail, and in 
many ways. 

Know then that your customer no 
longer believes that the actors stand 
behind your screen and do their stuff. 
He knows that the singers, the musi- 
cians, the actors, have all done their 
bit in the studio before the mike, and 
that when the result has been deliv- 
ered to your theatre, it is what is 
popularly known as "canned." All 
your customer wants, and he should 
reasonably expect it, is a credible ef- 
fort at satisfactory reproduction. 

Synchronized Apparatus 

It doesn't make any difference if 
your apparatus is the most expensive 
(I won't say the best) or one to fit 
the purse of the house. Whether it 
cost $14,000 or $1,400, if you as man- 
ager, demand and get a careful first 
adjustment of your machine, you've 
gone a long way toward satisfying 
your patrons. 

Dropping the technical stuff— the 
more you know of it, the more it con- 
fuses you — let the engineer from the 
installing company do the worst work 
for you. Matching horns and cones, 
or both ; setting amplifier units so as 
not to overload the reproducers : 
matching tubes ; balancing input from 
pickups on both projectors, and clock- 
ing speeds of machines to maintain a 
constant pitch of music or voice. 

The other technical stuff on the 
power to run the apparatus, and 
stabilizing the current, ironing out 
hum and interference . . . that's 
also work for the engineer. 

On With the Show! 

Now we're ready. What do you do? 

Above all, DON'T whip and force 
each and every one of those $1,400 or 
$14,000 so that they roar out of the 
reproducers and knock your cash cus- 
tomers out of their seats. 

They know you have sound in the 
house. Your marquee banners tell 
them that before they come in, and 
when they sit down they expect to 
have it served to them intelligently. 

Your house owner may want to let 
the folks know what a wow of an 
apparatus he has installed for their 
amusement, or the engineer of the re- 
producer company would like to 
demonstrate how powerful a blast he 
can produce. 

Don't Let Them Do It! 

Have some consideration for your 
patrons' eardrums. 

And bear this in mind. 

Most of your patrons have a radio — 
wherever they go they hear it . . . 
stores, . . . lunchrooms, . . . 
barbershops ... all over . . . 
and now you give it to them. But, be 
careful. If you don't know what I 
mean, go in most any barbershop 
tired, worn, worried about 
your business . . . and expect to 
get a comfortable quiet shave. You'll 
soon find out — if the radio is turned 

A volume that reaches you moder- 
ately to the back of the house, will 
be mighty thoughtful of the patrons 
down front, and far more entertaining. 

I recently met an engineer who told 
me he had just had a curve chart 
made of his ear to show the suscep- 
tibilities to cycles and pitch. Which 
was all very interesting. But he had 
evidently listened to cycles, fre- 
quencies, beats, blasts and what have 
you, until he developed a "tin ear." 
Music and reproduction didn't mean 
much to him unless it hit him full in 
the face with a wallop ! 

Don't think your customers all have 
"tin ears." 

Unbalanced Projectors 

Reel one ends, and we fade to reel 
two. The volume, which had been 
comfortably loud, drops considerably, 
and looking into it we find that Pro- 
jector No. 2 is a few feet further 
away from the amplifier unit than 
Projector No. 1. This made a longer 
pickup lead, adding more resistance 
and cutting down the energy delivered 
to the amplifier. 

I have recently listened to show 
after show in a house where this hap- 
pened. When the change was made 
to Projector No. 2 the power was 
boosted, and back to Projector No. 1 
the power was dropped. 

Somebody had to have a finger on 
the monitor button all the time. An 
engineer was present and I suggested 
that the pickups be balanced, so as 
to deliver the same energy from the 
fader box. 

Either he was too much engineer, 
or none at all, he argued that it 
couldn't be done, and that the opera- 
tor would have to compensate for the 
difference on the fader, each time he 
switched projectors. 

Which was a lot of boloney. If the 
machines can't be set, for example, so 
that point 7 on the fader gives the 
same volume for Projector No. 1 as 
for Projector No. 2, when reels change, 
more confusion would result. 

And if everybody, from the manager 
to the operators, gets confused . . . 
God help the talkies ! 

We'll take another angle. Both ma- 
chines are balanced for volume and 
we make a change of reels. The new 
reel starts off with a higher or lower 
pitch than the previous one. 

There are few families in these 
United States that do not own a 
phonograph, or have not at some time 
or other possessed one. And, they 
recognize the running down of a 

motor, or the winding up in the middle 
of a selection. 

I heard a change recently. In the 
first reel, just before the switch, a 
songwriter is playing the piano intro- 
duction to a new song he had written. 
In the opening of the next reel, he 
begins to sing ... a couple of 
tones lower than the piano part. There 
was a well-voiced groan from the 
crowd — almost community singing! 

Watch the speed of projectors . . . 
make them match ! 

Out of Synchronization 

It happens in the best of families. 

If it is in the first part of the reel, 
don't juggle with the record or speed. 
STOP, rewind and get away to a fresh 
start. But slide a record on your 
non-sync table and entertain the cus- 
tomers while you're doing it. 

I heard one operator jumping around 
on a record, trying to land the needle 
on the right spot, and succeeding in 
delivering an unholy effect from the 

If the trouble happens far in the 
record, or a scratch or crack causes 
the needle to jump out, or repeat 
cut out the sync table, and 
carry on with an orchestral record on 
the non-sync. You'll get by without 
getting any hoots from the crowd. 

Every Manager His Own Conductor 

One house manager seemed to take 
his daily exercise by running back 
and forth to the monitor button. 

If the action of a picture pepped 
up and the music became a bit louder, 
he cut it down ! When the music 
dropped down with a slowing up of 
action, back to the button, and he 
boosted the power. 

This same manager in a dialog 
picture cuts down dramatic scenes, 
and raises a whisper to a shout. 

And, what for? 

When the producers make their 
stuff, they pay a competent director to 
synchronize the music. He knows 
more about music in that one picture 
than the average house manager would 
' know if he ran sound for the rest of 
his life. 

The director arranges his stuff to 
fit the moods and action of the picture 
. . . why should you try to lead 
the orchestra, too? If you aren't satis- 
fied with the studio musical accom- 
paniment, why run sound? 

And the strange part is that the 
studio in nearly all cases, produces a 
mighty capable accompaniment. 

Overtures and Exit Marches 

Give them a worthwhile overture, 
and a snappy exit. 

In one house that opened and closed 
cold, I suggested this to a manager. 
He gave me a five minute dissertation 
on the fact that his patrons had 
radios — they heard radios — they heard 
good overtures over the radio. That 
when they paid to come in to his 
(Continued on paae 35) 

Page 14 

Projection Engineering, November, 1929 

New Theatre Light Control System 

Lighting Operator in Front of Curtain Controls Theatre Lights Through 

Series of Knobs 

ANEW system of controlling the 
lights of a theatre, involving 
new and unique principles and 
minimizing time, labor and 
valuable space, has been developed by 
the General Electric Company and 
installed in the new Chicago Civic 
Opera House. The lighting director 

(usually the stage electrician), hereto- 
fore unseen to the audience but vitally 
important to the success of the produc- 
tion, now leaves his position back- 
stage for the first time in theatrical 
history, and takes his place in front 
of the curtain along with the prompter 
and the musical director. 

Remote Control 

In front of the curtain, the lighting- 
operator will control the stage and 
house lighting as easily and as intelli- 
gently as the orchestra conductor now 
directs the orchestra. In front and 
on each side of him will be arranged 
dials, knobs, tumbler switches, indicat- 
ing lights, etc. By the mere manipu- 
lation of a single knob all the corn- 

Above: Color master of Selsyn 
transmitter. Left: Voltage regu- 
lator unit of Selsyn receiver. 
Right: Grand stage master con- 
trol of Selsyn transmitter. 

plexities of stage lighting will be con- 
trolled, lights of various colors fading 
and brightening at various points and 
at the proper moments. Scenes re- 
quiring complex lighting effiects such 
as sunsets, sudden thunderstorms, bal- 
lets, etc., will require no more effort 
in their control than is required to 
flick a lighting switch in the home or 
to turn a door knob. 

Advantages of New Method 

The advantages of the new method 
are manifold. Heretofore, the control 
of theatre lights was centralized in a 
switchboard back-stage which, in the 
larger theatres, sometimes was 40 feet 
long by 8 feet high. Arranged on this 
switchboard were rows upon rows of 
"dimmers" with large levers whose 
movement controlled the brightening 

Reactor and 
d i sc o n n ecting 
switch rack for 
Selsyn t h y r a- 
t r o n control 
equipment for 
stage and audi- 
torium lighting. 

or dimming of the various lights or 
groups of lights. The operations of 
these dimmers required much physical 
effort and agility, and many elaborate 
and ingenious mechanical schemes 
were often resorted to in order to sim- 
plify the work. Their manipulation 

made it necessary for the electrician 
to be at a point "off-stage"' where he 
could not see, except indirectly, the 
effects he was producing and where 
he had to rely on cues of words or 
sounds to inform him when it was 
necessary to change the lighting ef- 
fects. Such a switchboard is no 
longer necessary. 

The new method also follows the 
modern trend which makes simplicity 
an essential, especially in theatres. By 
eliminating the old bulky switchboard 
in the wings, more space is made 
available to stage operations, and co- 
ordination of activities results. 

The "Selsyn" and "Thyratron" 

The control scheme which makes the 
new method possible involves princi- 
pally the use of three important de- 
vices: the self -synchronous motor, the 
low-vacuum rectifying tube marketed 
under the trade name of "thyratron" 
and a new type of saturated-core reac- 
tor. Reactors have been used before 
in stage lighting but a new type had 
to be designed to fit the new system. 

The selsyn is a device resembling an 
ordinary electric motor in appearance 
and general construction. Contrary to 
the operation of a motor, however, the 
rotating element does not revolve at a 
high rate of speed, but moves slowly — 
rarely more than a complete revolu- 
tion. When two selsyns are intercon- 
nected electrically, the movement of 
the rotating element of one produces a 
corresponding movement of the other 
rotating element in the same direction 
and by exactly the same amount. It 
is by the use of these devices that the 
operation of the Panama Canal locks 
is controlled, and they are also used 
in this country for various purposes 
including the opening and closing of 
bridges, operation of elevators, etc. 

Function of Reactors 

One side of the voltage supply to 
each light or group of lights passes 
through one winding of a saturated 
core reactor. The other winding of 
this reactor is fed. by direct-current in 

Projection Engineering, November, 1929 

Page 15 

varying amounts from a pair of thy- 
ratrons. The amount of rectified cur- 
rent supplied by these thyratrons de- 
pends on the electrical relationship 
between the elements of each tube, and 
this is determined by the control de- 
vices governed by the lighting oper- 
ator. As the amount of direct current 
fed by the thyratrons to the reactor 
varies, the resistance of the reactor to 
the lighting supply load varies from a 
point where the lights are out, to full 

The immediate determination of the 
relationship of the elements of the thy- 
ratrons is through the agency of de- 
vices called phase modulators. There 
are two of these for every individual 
lighting circuit, one for use during the 
present scene and the other for the 
purpose of "setting up*' the next scene. 
The operation of the modulators is. in 
turn, governed mechanically either by 
the action of a selsyn or by knobs in 
front of the lighting operator. 

By manipulating the knobs on the 
individual modulators, the lighting op- 
erator could control the lights, but it 
would involve the operation of a pos- 
sible 141 knobs in the case of the Chi- 
cago Civic Opera House, as there are 
that many lighting circuits on the 
stage. By the use of the selsyns, how- 
ever, it is possible to govern all the 
lighting circuits through one knob, or 
to split the control into major and 
minor divisions, depending on color, 
location and function, each group in 
turn controllable through the agency 
of a knob. This is done in the follow- 
ing manner : 

Master Control 

The grand master knob controlling 
all the lights on the stage electrically 

Lighting-directors' control board for Selsyn thyratron control equipment 
for stage and auditorium lighting. 

controls the movement of the rotating 
element of a grand master selsyn. This 
selsyn is electrically connected with 
selsyn governing not only the major 
and minor groups of lights, but also 
the individual modulators for single 
lighting circuits. Therefore, move- 
ment of the ground master selsyn's 
control knob causes all the selsyns 
operating the modulators to move in 
conformity with it, and the modu- 
lators, preset in accordance with the 
recpiiremeuts of the scene, operate to 
control the lights. If. however, indi- 
vidual control of any major or minor 
group or individual lighting circuit is 
desired, the knob in epiestion may be 

Rack containing 
banks of thyra- 
trons for Selsyn 
control equip- 
ment. The thy- 
ratron is a form 
of "grid-glow" 

turned and the resulting movement 
does not interfere with any of the 
other circuits. 

There are 141 individual stage light- 
ing circuits in the new Chicago Civic 
Opera House. Each of these circuits 
includes lights of but one of the four 
colors used on a theatre stage — amber, 
white, blue and red. A typical circuit 
may cover the amber lights at one 
side or the center of the footlights, 
the red lights in one of the light 
bridges, or the white lights in one of 
the "pockets." These individual cir- 
cuits are grouped under the control of 
master knobs governing, for example, 
all the blue lights in the borders and 
footlights, all the amber in the pocket 
lights, all the white in the light 
bridges, etc. In addition, all the lights, 
of each color, no matter where, are 
controlled by a color master knob. 
Finally, all the color master knobs can 
be group-controlled by the grand mas- 
ter knob. The same system is fol- 
lowed with the "house" lights of the 
theatre, but in a much simpler form 
as the lighting circuits involved are 
comparatively few. 

Control Energy Involvel 

The energy involved in the control 
of any of the individual lighting cir- 
cuits is approximately one-tenth that 
consumed by a pocket flash light. The 
energy controlled, however, runs as 
high as 30,000 watts in a given circuit 
—more than half as great as the power 
ratings of the largest broadcasting sta- 
tions in this country. 

In actual operation, the lighting op- 
erator will preset the individual mod- 
ulators to create the desired lighting 
effect in the first scene and when the 
performance starts, the modulators 
will be connected in the circuit by 
means of a master tumbler switch. 
Varying the intensity of the lights will 
then be merely a matter of turning the 
grand master knob, or other knobs as 
(Continued on' page 31) 

Page 16 

Projection Engineering, November, 1929 

Public- Address and Centralized Radio 


1. The Power Amplifier, Power -Supply Unit and Fader Control 

By E. W. D'Arcy 

THIS particular subject has 
gained an unusually great 
amount of interest in the last 
eighteen months, due to the de- 
velopment of several forms of talking 
motion pictures. At the same time, 
there has been very little information 
relative to public-address systems, 
power supply, and associated equip- 
ment, available to the engineer not in 
the employ of one of the several lead- 
ing manufacturers. It is quite a prob- 
lem, and it would be impossible to at- 
tempt to cover all the angles in any- 
thing short of a text book. We will, 
therefore, content ourselves with con- 
centrating salient points into a group 
of articles to appear in subsequent 
issues of Projection Engineering. The 
following article deals with this sub- 
ject generally ; mainly with the power 
supply and actual amplifier unit, the 
best way to obtain maximum efficiency 
out of this equipment, and the minimiz- 
ing of hum. 

Several different electrical units, 
such as phonograph pickups, micro- 
phones, attenuation pads, etc., are used 
in public-address equipment, and for 
ease of discussion we will subdivide 
them and discuss each one indi- 

Combined Amplifier and Power- 
Supply Type 

A great many of the more popular 
amplifier units have their power sup- 
ply built in as an integral part of the 
complete unit. This system has its 
advantages where no great degree of 
amplification is occurring in the unit, 
or in the enclosure of the stage of 
amplification under discussion. How- 
ever, where a complete public-address 
amplifier is used with a high grade 
type of microphone the gain through- 
out the whole amplifier system is quite 
considerable, which means that the 
first stage of the amplifier becomes ex- 
tremely sensitive so a great deal of dif- 
ficulty is encountered from hum, due 
to pickup in filament leads, wires, and 
stray electromagnetic coupling. This 
can be overcome to a large extent by 
placing the audio transformers at a 
proper angle with respect to the power 
transformer. The angle is extremely 
critical and the transformer should be 
placed in its angle under actual condi- 
tions, the best way of doing this being 
to short circuit the grid of the tube 
preceding the transformer under hum 
adjustment to its cathode, then turning 
the amplifier on and adjusting the 
transformer for minimum hum output 
as shown on a hum meter. All the 

THIS is the first of a series of 
articles on Public-A ddress and 
Centralized Radio Systems by Mr. 
D'Arcy. Subsequent articles will deal 
with fader control systems, line balanc- 
ing, level-indicating devices, impedance- 
matching ; then centralized distributing 
systems, channel-selecting devices, re- 
lay control, and so on, completing the 
series with data on laboratory test 
equipment. — Editor. 

transformer cases should be grounded 
and, if possible, all wiring incased in 
iron pipe for shielding. 

In some of the better grade of pub- 
lic-address and theatrical amplifiying 
systems, separate power supply is in- 
corporated for each particular stage 
of amplification. This precaution is 
necessary due to the voltage drop 
through the choke coils and rectifier 
tubes. If a slightly gassy tube is used 
in one of the stages the increased cur- 
rent causes a drop in voltage on the 
preceding stages with a resultant 
amount of distortion. It is not neces- 
sary where voltage amplifiers are used 
and the impedances of the tubes are 
so high that no considerable amount of 
current is likely to be drawn in the 
plate circuit, but where a large amount 
of power is required in the amplifier, it 
is necessary to minimize the possibility 
of a voltage drop such as has just 
been mentioned. Consequently, this 
system has received the approval of 
the largest manufacturer of motion 
picture sound equipment. There is 
still, however, a considerable amount 
of difficulty arising from transient elec- 
tromagnetic fields. It would seem 

from the results obtained that the diffi- 
culties of this particular system are 
very much over-balanced by the su- 
perior quality obtained and the re- 
liablity of the equipment. 

Separate Power Supply 

Where portability is not a necessity 
and the equipment is being built for 
a permanent installation, to be oper- 
ated off the commercial lighting sup- 
ply available, a very much better type 
of equipment can be constructed by 
separating the power supply from the 
amplifier. This is a very excellent 
practice and can be accomplished quite 
easily. By this method it is possible 
to remove the power supply trans- 
formers far enough away so no great 
trouble is encountered due to stray 
electromagnetic fields and hum ; there- 
fore, this source of trouble can be con- 
sidered as eliminated with this type of 
apparatus. This particular design 
merely necessitates the building of a 
separate rack on which is placed all 
the power supply equipment, such as 
power supply transformers, filter 
chokes, rectifiers, voltage dividers, and 
the power control equipment. A small 
expenditure of money is required for 
this design but the additional expendi- 
ture is more than warranted in the 
improvement of results. The same 
warning holds true, however, that 
where a low impedance tube is used 
and there is a possibility of one of the 
tubes becoming slightly gassy and 
drawing an enormous plate current 
from surges of its applied grid voltage, 
a necessity still exists for separate 
power supply, especially, where push- 
pull stages are used. 

The author so far has not witnessed 

Fig. 3. Front view of a portable public-address amplifier. Pro- 
visions are made for its use with microphone, pickup or radio. 
Fading also can be accomplished. 

Projection Engineering, November, 1929 

Page 17 


;. 10,000 -n- (O.OOO-n. 

> A rinn __ 7 

\ AB23456T8 





Schematic dia- 
gram of the 
portable p.- 
power unit for 
a. a m p I i fi e r. 
The terminal 
numbers i n d i- 
cate the con- 
nections to be 
made between 
this unit and 
the amplifier. 

a commercial type of push-pull, low 
impedance, high output, stage of ampli- 
fication working without an unexplain- 
able high plate current. The plate 
current variation in this stage, using 
type-50 tubes, increases to as high as 
185 milliamperes from the normal 
level of 110 milliamperes when deliver- 
ing an output of 7 watts. This terrific 
increase in current makes it an im- 
possibility to operate the tubes off the 
same power supply as used for the pre- 
liminary stages. Fair results can be 
obtained, however, where push-pull 
stages are eliminated and the iron in 
the output transformer is operated far 
enough beyond its saturation point to 
become an effective impedance, thus 
aiding in choking out any transient 
gassy current which might occur. As 
an actual demonstration of this point, 
with the two type-50 tubes previously 
mentioned, the same identical tubes de- 
livered an output of 15 watts with an 
increase in the plate current of only 10 
milliamperes. This statement can be 

checked very easily in practice, the 
only necessity being that of an output 
transformer with enough iron and cop- 
per in it to insure good reproduction 
at high values of plate current. 

Portable Public-Address Amplifier 

An illustration is shown here (Fig. 
3) of a portable public-address ampli- 
fier with every facility included for 
operation from microphone, phono- 
graph pickup, and radio. Fading also 
can be accomplished between any of 
the three mentioned sources of supply. 
The mixer circuits, as shown in the 
schematic diagram of Fig. 1, are 
matched and built for a 600-ohm line 
impedance. Special designed trans- 
formers of an unusually high quality 
are used. However, even in this ampli- 
fier, the hum is still quite a consider- 
able element, and a compact amplifier 
of this type would not be practical for 
theatrical purposes. This particular 
schematic diagram has been subdivided 
into several separate sections — the 

power-supply unit being shown in Fig. 
2 — so that we may take up the discus- 
sion of each component section in sub- 
sequent issues. 

Input and Fader Controls 

The line input volume controls and 
fading controls are somewhat novel, as 
can be easily discerned. It is quite 
obvious that for good reproduction 
without attenuation of the higher fre- 
quencies, it is extremely necessary to 
have all the impedances of the system 
worked out correctly. For that reason, 
instead of merely short-circuiting the 
primary of one of the transformers for 
a volume control, a three legged T ar- 
rangement is used, by that means re- 
sulting in an unusually flat frequency 
response curve for any given degree of 
attenuation. The power output trans- 
former in this amplifier unit is so ar- 
ranged as to match the impedance of 
the following loudspeakers — 4, 8, 12 
and 16, or by using the tips of the 
speaker plugs for the output circuit, 
as shown, and plugging into the output 
jacks on the panel, further impedance 
reductions can be obtained down to 
where impedance matches are possible 
with the voice coil of a . dynamic 
speaker, which is approximately 6 

This transformer has been especially 
designed to withstand the quite high 
degree of current flowing through its 
primary and still give an excellent fre- 
quency response. Insulation is an im- 
portant factor in an output trans- 
former used in this manner, and trans- 
formers insulated for 1,000 volts have 
a disgusting tendency to break down 
unceremoniously, therefore, a primary 
requirement for a good output trans- 
former is that of high insulation value. 

A further discussion on output trans- 
formers will be taken up in a subse- 
quent issue. 


5000 -n- 

Fig. 1. Schematic diagram of the public-address amplifier, along with the switching arrangement, faders and pads. 

Page 18 

Projection Engineering, November, 1929 



500co 3!r i 

LINE gg t 

inz J 

* 3=> 

> oh: 

: "S 




50 2°OoJ" RE:PEAT 

doou} C0(L F0R 


24- 1DB. / 







Circuit containing pads for reducing line level in speech input equipment. 

Fader Controls 

There are several combinations for 
effective fading devices for fading 
from one circuit to the next. These 
devices range all the way from a 
simple potentiometer circuit up to a 
much more complex balanced fader 
control, and the efficiency and fre- 
quency response of this particular 
amplifier system can be affected a 
great deal by the fader characteristics. 

A typical fader circuit is shown in 
Fig. 3. This scheme for fading from 
one circuit to the next is most uni- 
versally used. Oftentimes the fader 
control is the only volume control 
used. This system of using a fader 
control for volume control is not very 
good due to the fact that the im- 
pedance presented to the primary of 





Tapered potentiometer type of 

fader; one of the simplest fader 


the input transformer varies consid- 
erably, and at high degrees of attenua- 
tion, the higher frequencies are greatly 
attenuated, resulting in a very dummy 
and barrelly quality of reproduction. 
Undoubtedly, the chief reason for the 
popularity of this type has been due 
to its economy in manufacture. A 
very marked improvement can be ob- 
tained by a properly designed fader 
control circuit. This fader control is 
shown in Fig. 4 and can be used as the 
major volume control with no great 

By a careful examination of the cir- 
cuit here shown, it can easily be ascer- 
tained by a properly designed fader 
absorption resistance R-l, the com- 
pensation resistors R-2 and R-3, which 
are operated manually on the same 
control knob, maintain the impedance 

presented to both the pickup device 
and the input amplifier at substantially 
the same level. This system, therefore, 
allows .a very fine degree of volume 
variation with a hitherto unknown 
superior quality of reproduction where 
fader volume controls are used. It 
is a little known system, and has re- 
cently been developed by the author. 
This particular type of control is now 

Constant Impedance Input Volume 

In the average broadcast or public- 
address system, a need is oftentimes 
felt to equalize the volume level from 
different lines coming into the central 
control panel. Ordinarily, this sort of 
thing is either accomplished by a pre- 
determined attenuation network, such 
as shown in Fig. 5. This type of pad 
is arranged to give a previously ar- 
ranged degree of attention. It then 
becomes necessary to incorporate a 
finer degree of volume control, which 
has to be adjusted for the difference 
in line levels, as volume control No. 
2. This control is quite necessary for 
satisfactory monitoring, although the 
system, if made sufficiently variable, 
is the most ideal system of input vol- 
ume regulation. 

It is quite easily recognizable that 
the balanced network, as shown in 
Fig. 5, would be difficult to produce 
mechanically at a price within reach 
of the average user. For this reason, 
a new type of volume control has 
been devised, shown in Fig. 6, making 
use of the familiar T-type attenuation 
pad. The controls in this system are 

instanteously variable, and they 
move at the same time so that a very 
fair degree of compensation is reached, 
and the pad does not vary from its 
estimated impedance at all degrees of 
attenuation more than 5%. This 
variation is easily allowable, as a very 
small amount of reflection takes place 
when the percent of error is held to 
this factor. 

The typical public-address system, 
shown in Fig. 2 gives one a very good 
idea of the placement of both the 
attenuation networks and the fader 
controls. Formulas are presented 
here (see Fig. 7 and Table I) for the 
easy determination of the constants 
to be used in this filter pad. The con- 
stants are worked out for pads from 
1 to 40 dbs. in attenuation. It is not 
figured in impedances, however, as 

/ f \ 
B-R2 B-R1 B-R3 



A constant impedance fader con- 
trol. There is no appreciable at- 
tenuation of the higher frequencies 
with this arrangement. 

these can be easily computed by multi- 
plying the quantity designated under 
the heading as K* (2Z). This 
formula is used for the Y-leg in this 
attenuation network. For a T-type 
pad, the formula and constants herein 
presented can be easily changed to the 
impedance used by merely multiplying 
X fc by the impedance which it works 
into and out of. 

Constant Impedance Speaker Vol- 
ume Control Systems 

For variation of the volume output 
from the public-address amplifier, 
there oftentimes is required several 
different degrees of volume such as 
might be encountered where several 
banks of loudspeakers are operated 

500 w 



500 co TO 

200 W 

200 oj T-PAD 





500 to T- PAD 



500,000 oj IN 

Low level, speech input amplifier, showing method of matching line levels by 

means of T-pads. 

Projection Engineering, November, 1929 

Page 19 

simultaneously off the same trans- 
former output. The matching of im- 
pedance in this circuit is very neces- 
sary for best reproduction, and it is 
quite easily recognizable that it is im- 
possible to have a different input vol- 
ume control with its associated ampli- 
fier for every degree of output volume 
required. There are no such devices 
on the market at the present time, but 
the author understands that one will 
soon be available for use in conjunc- 
tion with amplifiers to fulfill the re- 
quirements herein mentioned. This 
volume control is the same as the 
input volume control herein described, 
with the exception that it is designed 
to fulfill the requirements of the indi- 



K =T 

Y K 

X K 



Y K 

X K 








































































• 951 







• 0225 













• 598 









































































































Circuit diagram of speaker distributing system for public-address installa- 

vidnal user, that is, if he has a bank 
of four speakers connected in parallel 
(See Fig. 8), where the impedance of 
one individually might amount to say 
4,000 ohms, the total impedance of 
this bank, therefore, would amount to 
1,000 ohms. This condition requires 
the installation of the correctly de- 
signed attenuation pad. It is easily 
understandable that for this reason no 
great individual stock at any partic- 
ular impedance will be available, but 


V-2z(-^)"2z(yk). K.ANTI-LOGtff). Y-az^-ZzM 

Complete design 
data for bilater- 
ally symmetri- 
cal pads or at- 
tenuation net- 

manufacturers or engineers installing 
equipment of this nature can make 
known their requirements and they 
can easily be fulfilled. 

For the use of the average installa- 
tion a transformer with several differ- 
ent output impedances is required. It 
is impossible to make any particular 
conjectures for the typical installation, 
other than to say that the transformer 
displayed in public-address installa- 
tion pictured in Figure 3 has an im- 
pedance range of the following : The 
first tap 210 ohms ; the second tap, 280 
ohms ; the third tap, 420 ohms, and the 
last tap, 840 ohms. Then, any further 
variation in impedance required could 
be obtained by using the tips of the 
plugs to make connecting points with 
the switch arm itself, and further im- 
pedance variations could be obtained 
down to even the required impedance 
to match the voice coil of one dynamic 
speaker, which is equivalent to 6 ohms. 
A system of this range is really ex- 
tremely necessary, unless the designer 
stipulates the use of constant im- 
pedance volume controls,, and the 
speaker banks into which they are to 

(To oe continued) 

Recording on a Steel Wire 

Numerous Advantages Found in Use of Novel Recording System 

AN eastern concern, which pro- 
duces canned radio programs : 
the sound is recorded on a film, 
have employed steel wire for 
pre-recordings in order to obviate the 
necessity of recalling an orchestra to 
play over a piece of music, and inci- 
dentally, to save film which might 
otherwise be wasted. 

The program is first impressed on a 
moving steel wire. The operator 
listens in on the wire while the pro- 
gram is being run, If there is an error 
of any sort, or over-modulation, the 

undesirable part is "erased" by re- 
versing the direction of the moving 
wire and running it through a mag- 
netic field. The passage is then played 
over again, commencing, of course, 
from a silent area. 

When the entire program is im- 
pressed on the steel wire it is then re- 
recorded on to the film. For this 
operation the wire is run through a 
magnetic pickup, in the form of a 
solenoid, and the resultant electrical 
current fed into a standard vacuum 
tube amplifier which modulates the 

usual light source. Any attenuation or 
over -emphasis of frequency in the orig- 
inal recording is brought to the proper 
level through a gain control. 

The wire will faithfully hold a re- 
cording for more than a week, so that 
it is not necessary to make the re- 
recording immediately after the pro- 
gram run. 

The same wire can be used over and 
over again as there is no form of 
wear. Of course, it must be "magnet- 
ically erased" before another program 
is recorded. 

Page 20 

Projection Engineering, November, 1929 

"Narrowcasting" with the Photophone 

Transmitting Music Over a Beam of Light — a Projection Medium 
With a Wavelength in the Vicinity of tifty-Thousandths of an Inch 

SOUND becomes visible and light 
is made audible by an interest- 
ing laboratory development re- 
cently exhibited in Schenectady 
by John Bellamy Taylor, consulting- 
engineer of the General Electric 

A large group watched a beam of 
light travel silently about the room 
only to break into music as it hit a 
mirror target. When the light left 
the target or when it was intercepted, 
the music stopped. This was a demon- 
stration of what Mr. Taylor has 
chosen to call "narrow-casting" to 
distinguish it from radio broadcasting. 
Mr. Taylor has produced a photophone 
on old principles, utilizing for his 
purpose the perfected photoelectric 
cell, electrical pickup and newly de- 
veloped amplifiers and sound repro- 
ducers. The idea of sending music 
over a beam of light was demonstrated 
by Alexander Graham Bell 50 years 

In demonstrating the photophone, 
Mr. Taylor put on phonograph records 
which were sent over the light beam 
to the transforming and reproducing 
elements. When he held his hand in 
the path of the beam, the music 
stopped but as he allowed the light to 
filter through his fingers the sound 
began and increased in volume as he 
spread his fingers. A cardboard disc 
with holes of various sizes from a pin 
hole to a hole an eight of an inch in 
diameter, gave varying degrees of 
sound volume. 

Mr. Taylor also reproduced the 

Jnhn B. Taylor with the trans- 
mitting apparatus for projecting 
sound over light waves. 

sound of a burning match. When he 
struck a match there was a rattling, 
cracking sound, lasting during the 
combustion of the chemicals. The 
burning wood gave off little sound. 

Description of Photophone 

The photophone consists of a sound 
source ; that is, a phonograph record 
or a speaker at a microphone. Mr. 
Taylor generally utilizes a phono- 
graph with an electrical pickup by 
means of which the recorded music 

Mr. Taylor con- 
trolling th^ 
sound intensity 
with a sheet of 
paper. The re- 
ceiving appa- 
ratus is seen at 
the left, the 
turntable, pick- 
up and trans- 
mitter at the 

is transformed into electrical current. 
This energy is lead to a mirror, one 
thousandth of an inch square which 
is delicately suspended in a magnetic 
field by means of wires. At one side 
is an ordinary automobile headlight 
lamp, the light from which is focused 
on the tiny mirror. The mirror, quiv- 
ering in tune with the electrical cur- 
rent focuses the light to a lens through 
which the beam, pulsating at the fre- 
quency determined by the music on 
the record, is projected to a target 
focusing mirror or a lens. At this 
point, another transformation must 
take place ; the light must be con- 
verted to sound. The mirror, or lens 
focuses the light on the photoelectric 
cell which responds very speedily to 
every infinitesimal variation in light 
intensity. The photoelectric cell trans- 
forms the light into electrical energy 
and this, after amplification, passes to 
a loudspeaker where another trans- 
formation occurs and the energy be- 
comes sound. 

The difference between sending 
sound over a beam of light and by way 
of radio is simply one of degree, the 
physics in both cases is the same, 
except that quite different trans- 
mitting and receiving devices are used. 
In the case of light, frequencies of 
several hundred trillion per second 
give wavelengths of the order of a 
fifty-thousandths of an inch. The 
broadcast waves, which are also these 
changing forces in space, are from 
200 to 500 meters in length ; in other 
words, the broadcast wave is a half 
mile to a mile in length compared to 
the light wave of fifty-thousandths of 
an inch long. The long wave of com- 
paratively low frequency spreads out 
in all directions, whereas the beam 
of light is essentially a straight line 
affair and, with condensing lens, beam 
forming lens, or reflector, can be con- 
served and sent to quite a distance 
without any substantial spread. The 
broadcast wave will bend around ob- 
structions and pass through walls, but 
the light wave will not bend because 
the wave is so short in comparison 
with the size of the obstruction and 
it will pass through only such solids 
as are transparent. 

Uses for the photophone have not 
been indicated as yet. Mr. Taylor has 
been able to pass a light beam during 
daylight across a street, from one 
office to another. At night the beam 
may be projected three or four miles, 
provided a strong enough light source 
is used and a suitable large target 
mirror adopted. Wartime use of the 
light beam as a system of communi- 
cation between fixed points, where 
radio or wire communication is im- 
practical or impossible, also suggests 

Projection Engineering, November, 1929 

Page 21 

Notable Advances in the Motion- 
Picture Industry 

Abstract Report of the Progress Committee of the S.M.P.E. 

THE most important items of 
progress during the past six 
months have been the extensive 
use of all-color sound pictures, 
or pictures with extensive color in- 
serts, and several demonstrations of 
enlarged projected pictures by the use 
of film wider than 35 mm. 

Only two-color subtractive processes 
are at present in vogue, and in one 
process extensively employed two dye 
images are produced in a single layer 
film by imbibition. Although some 
three color imbibition films have been 
prepared, they have not been publicly 

To date only one type of wide film 
lias been put on the market ; this being 
70 mm. wide. Comment of the trade 
has been most enthusiastic with re- 
gard to its suitability for scenics and 
news events, but it is apparent that a 
new photographic technique is required 
to secure more pleasing perspective in 
the case of photoplays. Difficulties in- 
volved in the more universal adaption 
of the wide film are : the present lack 
of standardization of size, the neces- 
sity for greater illumination at the 

By J. I. Crab tree 

projector aperture and the prevention 
of film buckle. 

Studios in Hollywood are now pro- 
ducing only about 5% of silent pic- 
tures. When it is considered that only 
one year ago the first dramatic pic- 
tures were shown before the society, 
notably, "The Singing Fool." the re- 
markable progress made since that 
time is apparent. There has been a 
steady improvement in the quality of 
sound reproduction, notably in the 
theatre, but in many cases the quality 
in the theatre falls far short of that 
which the film is capable of producing 
when it leaves the studio. Much still 
remains to be done in the way of im- 
provement even with the best of re- 
cording. With the high quality music 
given by the modern radio receivers 
the public is realizing that the average 
theatre music is not equal in quality 
to that emanating from their radios at 

Notable advances in studio tech- 
nique have been: — (a) the tendency to 
use a minimum number of microphones 
and eliminate "mixing:" (b) the 
silencing of cameras by means of in- 

sulating coverings thus permitting 
greater freedom of camera location : 
(c) the tendency to use more live 
studios so as to simulate more closely 
natural sounds; and (d) the non- 
simulateous recording of scene and 

A noteworthy advance in repro- 
ducers has been the introduction of 
the condensor or electrostatic repro- 
ducer consisting of a rubber dia- 
phragm coated with aluminum foil and 
stretched across a metal grid. Apart 
from the high quality resulting, the 
reproducer occupies no more space 
than the average screen and can be 
raised and lowered just as easily. 

No fundamental advances have been 
made in the field of stereoscopic mo- 
tion pictures and although some of 
the sponsors claim that their wide film 
processes give stereoscopic effects they 
are at the most pseudo-stereoscopic. 
A much higher order of relief is notice- 
able in many of the pictures in color. 

Although color pictures .have been 
televised during the past six months, 
the probability of television usurping 
the present motion picture in the im- 
mediate future is very remote. 

Testing Characteristics of Loudspeakers 

Special Sound-Proof Room and Revolving Microphone Employed 

STRANGE to say, the problem of 
getting better sound reproduc- 
tion from loudspeakers is best 
studied in a room especially de- 
signed and built to reduce sound re- 
flection as much as possible. 

To step into a room where sound 
reflection has been eliminated, or as 
nearly so as scientific knowledge can 
accomplish that end, is like stepping 
into an entirely new world. The first 
impression gained upon entering such 
a room is that of having left some- 
thing behind. If one were to sit per- 
fectly quiet for at least five minutes, 
an entirely different feeling becomes 
apparent. The first sensation is that 
of having one's ears straining to catch 
sounds to which they have been ac- 
customed outside the room. Failing 
in this, hearing is concentrated upon 
one's breathing, rustling of clothes, 
scraping of feet or shifting of position 
until these small noises which we 
rarely hear in every-day life become 
so magnified by our concentration that 
they annoy us very nearly as much as 
the boom of a cannon or a clap of 

All of this is highly interesting, you 
may remark, but what need can there 

be for a sound-proof room and how is 
mankind benefitted by experiments 
performed in it? There are many 
reasons. First of all, experiments per- 
formed in sound-proof rooms make it 
possible to design theatres possessing 
perfect acoustics. 

A Room Within a Room 

At the Stromberg-Carlson plant in 
Rochester, there has been built a 
special acoustics room, as nearly 
sound-proof and as nearly devoid of 
reverberation as possible. Actually, it 
is a room within a room with two 
heavy doors to prevent extraneous 
noises from entering through this 
means of access and it is here that ex- 
tensive loudspeaker tests are con- 
ducted for the purpose of determining 
means by which speakers may be con- 
stantly improved. 

The problems confronting the engi- 
neering staff in designing the room 
and associated testing apparatus were 
many and interesting. First of all, it 
was found necessary to conduct these 
loudspeaker tests in a room free from 
all sound except that produced by the 
speaker itself : hence, the necessity for 
the sound-proof room. The next step 

was to eliminate as far as possible 
reverberation inside the room for, since 
it was desired to measure sound pro- 
duced by the speaker, echoes caused 
by sound reflected from walls, ceiling 
or floor could not enter into the cal- 
culations. The problem is one of pre- 
venting sound reflection. In this 
room the side walls are arranged with 
heavy drapings of hairfelt. hanging at 
fantastic angles so as to scatter, rather 
than reflect the sound it does not ab- 
sorb. This tends to effect a more uni- 
form distribution of sound pressure 
within the room. The irregularity of 
the drapes does not materially affect 
their absorbing quality. 

Though a little off the line of dis- 
cussion, it is interesting to note that 
absorbent surfaces such as hairfelt, 
damp out .the sound energy reaching 
them by frictional conversion into heat 
within the pores of the surfaces. Of 
course, the heat thus generated can be 
measured only with the most delicate 
instruments and there is little danger 
of it ever being possible to create 
sufficient volume of sound that will, by 
its absorption in such a surface, make 
itself apparent to the sense of touch. 
(Continued on page 34) 

Page 22 

Projection Engineering, November, 1929 

Mechanics of the Talking Movies 

An Insight Into the Actual Processes of Sound-Picture Production With 
Some Critical Comment on the Technique Employed. 

By J. Garrick Eisenberg* 

WITH the advent of sound, a 
new and highly involved 
technique has been introduced 
into the . production and pro- 
jection of motion pictures. Where pre- 
viously the major problem of photo- 
graphy and projection alike was 
simply that of proper lighting, the 
joining together of sight and sound in 
the medium of talking pictures has 
introduced so many additional compli- 
cations, that the art now bears little 
resemblance to its former modest self. 

Perhaps the brunt of the labor of 
carrying on under these new and un- 
familiar conditions has fallen to the 
projectionist ; thrown willy-nilly into 
a situation which required him to 
master, overnight almost, the techni- 
calities of a highly specialized science, 
he has had little opportunity to ac- 
quire other than the most superficial 
knowledge of the principles underlying 
this new medium. 

Since the projectionist is a most im- 
portant factor in the process of actual 
audience presentation, it is imperative 
that he have as full a grasp of these 
principles as possible, if he is to 
achieve the best results with sound 

One of the present-day weaknesses 
of the business lies in the frequent 
spoiling of good recordings by poor 
manipulation or carelessness in the 
booth. On the other hand, a projec- 
tionist who is familiar with the im- 
perfections of recording can often 
cover up spotty, irregular sound 
tracks, and secure quite adequate re- 
sults from them. It is believed, 
therefore, that a discussion of the 
processes involved in the making of 
talking pictures may be of material 

* Recording Engineer, Tiffany Studios. 

VERY little information has 
been published on the techni- 
que of speech and musical 
recording in motion-picture 
studios. Of the data offered, little 
of it has been of a nature that would 
prove valuable to Projectionists. 

Mr. Eisenberg, a Recording Engineer, 
presents here an article covering those 
very phases of sound recording that 
Projectionists have been seeking to 
learn more about. 

Undoubtedly, the details offered, will 
assist many Projectionists in getting 
the most out of their film runs. — Editor. 

benefit to the projectionist in assisting 
him to a fuller understanding of their 
present limitations. The circuits and 
equipment used in recording sound 
have been described in these pages 
previously and will not require further 
treatment here ; the main purpose of 
this article will be to outline the ac- 
tual routine of sound-picture produc- 

Balancing of Sound Levels 

One is apt to lose sight of the fact 
that motion pictures are after all, a 
purely mechanical medium. In pro- 
duction, the various bits of action bear 
about the same relationship to the 
smooth finished picture as does the 
raw material of any other manufac- 
turing process. For example, one 
morning's work may include an elabo- 
rate banquet shot, and immediately 
following, a heavy love scene between 
the hero and his lady* the respective 
sequences being separated perhaps sev- 
eral thousand feet in the story. The 
reasons for this jumping about are 
manifold : the set — the movie equivalent 

A typical "long shot," cabaret scene in "Woman to Woman." (Tiffany- 
Stahl). The microphones can easily be cheated into the background of this 
sort of scene. One is shown in the middle foreground, disguised as a hang- 
ing lamp. Others are cheated in alongside chairs, etc. 

of scenery — may not be ready for the 
next sequence, the characters may not 
be up in their lines, or there may be 
last minute /changes in the iscript. 
Any one of a number of other reasons 
may obtain, including those of tem- 
perment. The actors are, of course, 
concerned only with the immediate 
business in hand. The director, how- 
ever, must film each bit with a 
wary eye to its relationship to the 
whole picture perspective. Tempo of 
action must be carefully watched, 
the lighting of the characters, which 
determines mainly how they will look 
to the cameras, carefully planned out, 
and a thousand other details of pro- 
duction taken care of. 

It was a difficult enough process in 
the silent days ; with the addition of 
sound it has become an intricate one. 
Now, the balancing of sound levels in 
accordance with the dramatic value of 
a scene adds another complication, for 
again the complete perspective is the 
important one. The sound recordist 
may be an excellent technician, but if 
he lacks this sense of perspective he 
can ruin entirely the dramatic effects 
for which the director is striving. If, 
for example, the amorous wooing of 
the lovers is shot at nearly full track, 
what more can be done for the ban- 
quet scene or the rest of the heavy 
fireworks? The recordist, therefore, 
usually analyzes the shooting script 
for dramatic values before production 
begins, and assigns arbitrary levels to 
each scene. In this manner fairly con- 
sistent values can be maintained 
throughout the picture, even though 
several weeks may elapse between 
shots of related sequences. If his 
dramatic interpretations are poor, 
however, or through carelessness he 
overlooks the initial levels, then of 
course the sound track will be jumpy 
when the scenes have been cut into 
their proper continuity in the com- 
pleted picture. 

Each day the rushes of the previous 
day's shooting are reviewed in the 
projection room and checked for qual- 
ity of photography and sound ; if it is 
not satisfactory for any reason, the ac- 
tion is retaken. Unfortunately, in the 
matter of levels, it is difficult to judge 
comparatively until the related se- 
quences have been assembled together. 
Thus it often happens that irregulari- 
ties in this regard are not obvious un- 
til the picture has been cut. By this 
time, shooting has probably finished 
on the picture, and rather than incur 
the expense of calling back the com- 
pany to retake the bad scenes, and 
setting his releasing program behind, 
the producer will pass the picture 

Projection Engineering, November, 1929 

Page 23 

Front view of a 
typical form of 
mixing control 
cabinet. The 
schematic dia- 
gram is shown 
on page 24. 


Sometimes the levels can be made 
to coincide more smoothly by re-re- 
cording the sound track so as to bring 
up the low passages, or where neces- 
sary, to cut down on the higher levels. 
This is accomplished by running the 
track through the projection machine 
and taking the output of the projection 
amplifier off to a recording amplifier, 
and an entirely new sound track made. 
The picture is run off at the same 
time, and the recordist, watching the 
picture action and monitoring the 
sound track, can manipulate his gain 
control to bring about the desired in- 
creases or decreases in level. The 
process has some advantages however ; 
some loss of sound quality usually fol- 
lows with such film transfers, and the 
ground noise ratio is increased when 
bringing up the low portions. If the 
jumpiness is not too flagrant therefore, 
the film may be sent out in the fond 
hope that the theatre projectionist will 
take care of whatever slight lapses 

Another and perhaps more serious 
defect of sound production methods re- 
sults from the practice of making all 
the camera shots of the action at the 
same time. In silent productions, a 
brace of cameras are set up at the 
proper distance for the 'long shot,' 
which establishes the locale of the ac- 
tion mainly. Then the action is gone 
through again with the cameras moved 
in closer for the medium and close-up 
shots, which cover the more intimate 
details of the action. In sound pro- 
ductions, however, long, medium, and 
close shot cameras are set up at vary- 
ing distances to cover the different 
phases of the action, and all grind at 
the same time. This means that the 
microphones must be placed a con- 
siderable distance from the action, for 
they must be out of the picture of 
course for all cameras ; the long shot 
covering the widest visual area is the 
determining factor in this placement 
of mikes, for the close-up and medium 
shot cameras, with their fairly re- 
stricted area of vision, ordinarily 
would permit bringing them -a good 
deal closer to the action. 

Placement of Microphones 

In order to record the dialogue with 
sufficient body to preserve its natural 
close-up quality, the microphones 
should be placed at a distance not ex- 
ceeding six feet. Otherwise, unless 
they are spoken directly into — which 
the exigencies of the action usually 
makes nonfeasible — a somewhat thin 
quality of recording results. This is 
permissible for long shot camera an- 
gles for it actually helps create the il- 
lusion of optical depth on the screen. 
For the close-up shots, however, the 
opposite effect is desired ; here the im- 
pression created is that the action has 
been moved up closer to the audience. 
Unless the sound charges accordingly, 
however, the illusion will be an im- 
perfect one. Of course rhe track can 
be re-recorded after long shots and 
close-ups have been pieced together in 
the final cutting, but even though the 
volume of the close-up accompaniment 
is brought up, the result is an unnat- 
ural shouting effect on the part of the 
characters. To give this the effect of 
an aural close-up the microphones 
must be reasonably close to the action 
in recording; by reason of these 
limitations some directors eliminate 
the long shot entirely whenever pos- 
sible. This is obviously not the cor- 
rect answer to the problem, however, 
because it means the sacrificing of pho- 
tographic values which the wide 
sweep of the long-shot cameras afford. 

The better procedure is to take long, 
medium, and close angles as entirely 
separate shots, as was done in the days 
of silent productions. 

The present method was brought 
about by the belief that the dialogue 
of a sequence could not be cut up 
without losing parts of it in the cut- 
ting. It was also maintained that the 
proper levels of sound for close-up and 
long shot of the same action could 
not be accurately gauged nor matched. 
For a time in the very early stages of 
sound productions these reasons were 
substantially true, but only by virtue 
of a crude and inadequate technique 
in recording, and in cutting of the pic- 
ture. With the refinement of method 
which has come with larger experience, 
however, there no longer exists any 
reason — except the very short-sighted 
one of greater speed in production — for 
adhering to this system, yet it con- 
tinues to prevail at a number of 
studios. Perhaps this is partly due to 
the fact that directors as a whole, 
have as yet no very clear conception 
of the mechanics of sound and are, 
therefore, reluctant to modify their 
original methods.' As more of them 
acquire a better understanding of what 
can be done with sound in the hands of 
competent technicians, we can look for 
a change in production methods result- 
ing not only in better quality of sound 
accompaniment, but in better photo- 
graphic values also. 

While the latter may seem to have 
no connection with sound, it is pointed 
out that a freer use of long-shot cam- 
eras must inevitably result in better 
photographic composition. Clever 
manipulation of the microphones into 
the backgrounds can be accomplished 
in this type of shot, without much dan- 
ger of detection by the camera. Some- 
times the long shot can even be shot 
silent, and the sound scored in later ; 
the slight loss of synchronism which 
may follow is not readily noticeable 
when the characters are some little 
distance from the camera. Then, with 
the long shot out of the way, the mi- 
crophones can be brought closer to the 
action for the more intimate shots, to 
take advantage of the better pickup 
conditions afforded thereby. This is 
the method used by the more enlight- 


Method of scor- 
i n g musical 
background into 
sound track. 
The output of 
the p rojection 
amplifier goes 
to the mixer 
panel instead of 
the loudspeak- 





cr < 



Page 24 

Projection Engineering, November, 1929 

ened director, and the added excel- 
lence of the product obtained more 
than compensates for the somewhat 
greater length of time necessary for 
setting up the cameras separately for 
the different shots. No doubt this 
practice will become standard in time 
at all studios ; when this desirable con- 
dition has been brought about perhaps 
the projectionist will no longer find it 
necessary to modulate the reproduc- 
tion to suit the picture's requirements. 
While present methods obtain, how- 
ever, it is obvious that this will re- 
main one of his more important func- 

Cutting and Editing 

The cutting and editing of the pic- 
ture is the final operation in produc- 
ing the finished story which eventually 
unrolls itself upon the screen in more 
or less smooth continuity ; it is an 
extremely important one. From the 
several hundred thousand feet of long- 
shot, medium, and close-up footage — 
the average for a feature length pic- 
ture — the subtle (sic) manipulations 
of the cutting room evolve the ten 
thousand odd feet of negative which 
constitute the story. 

The long shots are cut and matched 
and recut. to fit the close-up and 
medium shot scenes. Several takes of 
the same shot may be cut and matched 
together, to take advantage of the bet- 
ter dramatic action or photographic 
values of either one; sometimes entire 
sequences are cut out of the picture 
in order to speed up the action or 
shorten the picture. 

In these operations care must be 
exercised when cutting the sound track 
so that the cut takes place during a 
pause in the dialogue, or if there is 
a musical background, between rests ; 
in general the cutting of a scene with 
musical background is a very unsatis- 
factory process because of the diffi- 
culties entailed in matching musical 
phrases. The music is therefore 
'scored' into these scenes by making 
the sound track after the scenes have 
been cut. (See Fig. 1.) If there is 
also dialogue or other sound accom- 
paniment to the scene, the process is 
similar to re-recording. The original 

sound track is run off and its output 
taken to the mixer panel of the re- 
corder amplifier : the music to be scored 
in is cued to the picture action as 
shown on the screen : it is picked up 
by the microphones and brought to the 
mixer panel of the recorder amplifier 
also. The volume of the various sound 
accompaniments are then "mixed" to- 
gether in the desired proportions and 
fed into this amplifier, and recorded 
together in the form of a new sound 
track, which by this process is per- 
fectly synchronized with the picture. 


As the action chansres from long 
shot to close-up. or changes scenes, 
the musicians modify or amplify their 
efforts — the recordist likewise manipu- 
lating his gain control when necessary 
— or change smoothly over to a dif- 
ferent musical selection. This elimi- 
nates the possibility of cutting out or 
duplicating notes, or even entire musi- 
cal phrases, and of abrupt changes in 
volume, all of which are imminent 
clangers when cutting into an original 
sound track of musical recordings. 
Some studios still persist in this latter 
practice nevertheless. 

When entire sequences are cut out 
of a picture in editing it (sometimes 
the more that is cut out, the better the 
picture becomes) there are added pos- 
sibilities of abrupt volume changes. 
Technique in the cutting rooms is im- 
proving, however, and no doubt fur- 
ther experience will dictate a stand- 
ardized practice in cutting sound films, 
which will eliminate many of the 
present irregularities. 

Film Speed 

The remarks with reference to 
'sound films' can be taken as govern- 
ing production methods in general, 
whether the recording medium be disc 
or film track ; with discs, cutting from 
one sound track to another always 
means a re-recording job ; as pointed 
out, with film track, dialogue can be 
cut during a pause in the conversa- 
tion, the two tracks spliced together 
and then printed as one continuous 
positive. The minute lapse in the 
sound, where the two tracks are 

N2. 2 

© ® 

© AMP. © 

© AMR © 

© AMR © 

The circuit diagram of a three-channel mixing panel. The mixer is more 
or less a glorified fader system. 

patched together, is not detectable if 
the cutting is skillfully done. 

One other matter with relation to 
sound recording methods may be of 
interest to the projectionist. This con- 
cerns the uniformity of recording (and 
projection) speeds of 90 feet per 
minute, a matter on which some puz- 
zlement exists. The audio cut-off of 
sound systems in recording has been 
arbitrarily set at 6,000 cycles ; this is 
the highest, frequency considered neces- 
sary to reproduce in order to secure 
musical tones of good fidelity. Since 
the length of a 6,000-cycle sound wave 
is .003 inch, a speed of 18 inches per 
second (90 ft. per minute) is necessary 
to get this onto the film or wax. Ob- 
viously, of course, the reproducing ma- 
chines must be run at the same speeds 
or else the tone and pitch of the 
original recordings will be distorted. 
Since the sound must be in synchronism 
with the action, the cameras (and pro- 
jectors) must also be run at this same 
speed. In production, camera motors 
are electrically synchronized and in- 
terlocked with the recorder motors, pic- 
ture and sound thus being kept in step 
at the speed of 90 feet per minute. 

The normal speed of cameras in 
making silents was 60 feet per minute; 
at this speed 16 images per second 
pass the camera aperture. At the 
higher speed of 90 feet per minute, 24 
images pass the aperture* per second. 
The result photographically is an ap- 
parent slowing down of the action, be- 
cause it is spread over a greater foot- 
age. Since the sound recording re- 
quirements necessitate this speed, how- 
ever, the only possible compromise is 
to speed up the tempo of the action, 
and we can expect to develop in time 
a distinct technique in talking-picture 
action, differentiated entirely from 
that of either stage or silent pictures, 
and one whose increased tempo will 
enhance the dramatic values of sound 
pictures considerably. While this phase 
of the business may have only a vicar- 
ious interest for the projectionist, it is 
pointed out as another problem in the 
mechanics of sound-picture production. 

The Human Element 

The projectionist will realize from 
this discussion that the quality and 
degree of smoothness of the sound 
itself, will depend largely upon the 
functioning of the human equations 
necessary to the process. The limita- 
tions imposed are largely those of tech- 
nique, rather than of equipment ; the 
very necessary flexibility of production 
methods introducing serious errors of 
practice. The remedy, of course, lies 
in recognition of these defects, and in 
refinement and standardization of re- 
cording methods so as to overcome 
them. Meanwhile the burden of carry- 
ing on under present conditions falls 
largely upon the projectionist, and if 
he is at all worthy of his salt, he will 
make every effort to cover up by skill- 
ful handling of the gain controls, the 
present limitations of the art. 

Projection Engineering, November, 1929 

Page 25 

The S.M.P.E. Toronto Convention 

Wide Range of Problems Covered at Fall Meeting 
By P. A. McGuire* 

THE Fall meeting of the Society 
of Motion Picture Engineers, 
held at Toronto, Ontario, Oc- 
tober 7 to 10, was a conspicuous 
success in many particulars, and it 
is difficult to see how succeeding meet- 
ings of the Society are going to be any 
better or even as good as this oner 
However, the S. M. P. E. has had 
many highly successful meetings, each 
one differing from the other, but all 
with high spots which have established 
a record of successful achievements for 
the Society. 

It has been the good fortune of the 
S. M. P. E. to have had every success- 
ful development in the motion-picture 
field given an advance showing or pre- 
viewing at the convention of the So- 
ciety. Many showings have been made 
in color and practically every great 
system of sound pictures were given 
an early demonstration during the 
meetings of the S. M. P. E. 

Discuss Technical Problems 

While the papers on sound played a 
very important part in the program at 
Toronto, there was nothing excep- 
tionally new in this phase of motion- 
picture activities. 

For the most part the papers read 
dealt with highly technical problems 
of the making and showing of motion 
pictures. This is a long, long road 
starting out with "A New Method of 
Testing for the Presence of Hypo in 
Motion-Picture Film" by J. I. Crab- 
tree and J. F. Ross r Eastman Kodak 
Company, and "A Rapid Method of 
Determining the Degree of Exhaustion 
of a Developer" by M. L. Dundon and 
A. Ballard, Eastman Kodak Company, 
through to such papers as "The Mod- 
ern News Reel" by Harry W. Jones 
of R. C. A. Photophone, Inc., and "The. 
Illusion of Sound and Picture" by 
John L. Cass of R. C. A. Photophone, 

Somewhere in between subjects of 
this nature, practically the whole 
technical field of the motion-picture in- 
dustry was covered by such papers as 
"Theatre Acoustics" by S. K. Wolfe, 
Electrical Research Products, Inc. ; 
"The Optics of Motion-Picture Projec- 
tion" by Professor Arthur C. Hardy, 
Massachusetts Institute of Technology ; 
"Sound Projection Yesterday, Today 
and Tomorrow" by Rudolph Miehling, 
Paramount - Famous - Lasky Corpora- 
tion ; "The Film Perforation and 
Means for its Measurement" by W. H. 
Carson, Agfa Ansco Corporation ; "Sur- 
face Treatment of Sound Film" by 
J. I. Crabtree, C. E. Ives and O. Sand- 
vik, Eastman Kodak Company ; "A 
New Method of Blocking Out Splices 

^Advertising Manager. International Pro- 
jector Corp. 

in Sound Film" by J. I. Crabtree and 

C. E. Ives, Eastman Kodak Company ; 
"Characteristics of Loudspeakers for 
Theatre Use" by D. G. Blattner, Bell 
Telephone Laboratories, Inc. ; Rec- 
tangle Proportions in Pictorial Com- 
position" by L. A. Jones, Eastman Ko- 
dak Company ; "Optical Problems of 
the Wide Film" by Dr. William Ray- 
ton, Bausch & Lomb Optical Company ; 
"Some Practical Aspects and Recom- 
mendations on Wide Film Standards" 
by A. S. Howell and J. A. Dubray, Bell 
and Howell Company ; "The Wide 
Film from the Recording Standpoint" 
by C. A. Tuthill, Paramount-Famous- 
Lasky Corporation ; "A New Syn- 
chronizing Apparatus for 16 mm. Films 
With Disc Records" by Wm. Bristol 
Talking Picture Corp. : "Photographic 
Characteristics of Sound Recording 
Film" by L. A. Jones and O. Sandvik, 
Eastman Kodak Company ; "Some 
Fundamental Principles of Sound Re- 
cording and Reproduction" by Wm. H. 
Offenhauser, R. C. A. Photophone, 
Inc. ; "Studio Acoustics and Micro- 
phone Placement" by J. P. Maxfleld 
and H. C. Silent, Electrical Research 
Products, Inc. ; "Some Aspects of Re- 
verberation" by E. W. Kellogg, General 
Electric Company ; "Artistic Consid- 
erations in Sound-Film Production" by 
Joe W. Coffman, Audio-Cinema, Inc. ; 
"Film Numbering Device for Cameras 
and Recorders" by M. W. Palmer, 
Paramount - Famous - Lasky Corpora- 
tion ; "Some Properties of Chrome 
Alum Fixing Baths" by J. I. Crabtree 
and H. A. Hartt, Eastman Kodak 
Company ; "Water Cooling of In- 
candescent Lamps" by Dr. Newell T. 
Gordon, General Electric Company : 
"Operating Characteristics of High In- 
tensity Arcs" by A. C. Downes and 

D. B. Joy, National Carbon Company ; 
"A Studio Photometer" by J. L. Mc- 
Coy, Westinghouse Lamp Works; 
"Flexible Drive-Shafts — Their Appli- 
cation to Sound Pictures" by J. C. 
Smack. S. S. White Dental Company ; 
"The Microphone Boom and Its Use" 
by Lew Kold, Metro.-Goldwyn-Mayer 
Studios ; "Camera and Projector Ap- 
erture in Relation to Sound Pictures" 
by Lester Cowan. Academy of Motion 
Picture Arts and Sciences, and "Com- 
pensator for Movietone Production" by 
Gerald F. Rackett, Motion Picture 
Producers and Distributors Associa- 

S. M. P. E. Seeks Standards 

To anyone who is at all familiar 
with the technical side of the motion- 
picture industry, it will be obvious that 
the S. M. P. E. performs an important 
function by bringing so many men to- 
gether who are seeking to establish 
standards and bring about improve- 

ments in their own special field. Some- 
time the great producing and exhibit- 
ing executives of the motion-picture 
industry will be more keenly aware of 
the interdependence of the various de- 
partments of this industry, and give to 
the S. M. P. E. the support it has so 
well earned. 

The subject which seemed to be of 
the greatest interest to the Society was 
'wide films. Unfortunately those who 
were most active in developing this 
new and extremely important phase of 
the industry, were either too busy or 
were not quite ready to prepare a 
paper which would supply the informa- 
tion regarding wide films for which 
everyone is so anxiously waiting. 

While the wide picture is an accom- 
plished fact, it is in an experimental 
stage in some particulars, and those 
in charge of development along these 
lines, will be in a much better position 
to present a paper containing exact 
facts and figures for the next meeting 
of the S. M. P. E. 

Commerce Official Speaks 

Probably no paper presented at the 
Toronto meeting was of so much gen- 
eral interest as the one read by N. D. 
Golden, assistant chief, Motion Picture 
Division, Department of Commerce. 
This paper "The Sound-Film Situation 
in Europe" contained a vast amount of 
information relative to the export 
situation for American motion-picture 
films, and indicates that the S. M. P. E. 
take real interest in the practical 
economics of the motion-picture in- 

The social side of the meeting was 
a success from every standpoint. Hon. 
Samuel McBride, mayor of Toronto, 
welcomed the Society on Monday 
morning, and William F. Canavan, 
International President of the I. A. T. 
S. E. & M. P. M. O., made a splendid 
address on Tuesday morning. The 
banquet of the Society ou Wednesday 
night, which is always the outstanding 
social event of the S. M. P. E. meet- 
ings, also reached the high standards 
which have been established for these 

Dr. K. C. D. Hickman was Master 
of Ceremonies, and the speakers were, 
the Hon. H. J. Cody, chairman of the 
Board of Governors, University of 
Toronto. L. C. Porter, President, So- 
ciety of Motion Picture Engineers, 
Hon. J. D. Monteith, Provincial Treas- 
urer, Government of Ontario, J. I. 
(Continued on page 31) 

Page 26 

Projection Engineering, November, 1929 

Considerations in the Design of Audio- 
Frequency Apparatus 

The Properties of Core Materials, Methods of Winding Coils, the 
Air Gap — and Calculations of Distributive Capacitance and Leakage 


By C. H. W. Nason 
Part II 

Magnetic Properties of Core 

IN considering the magnetic proper- 
ties of a core material we must 
take into consideration the follow- 
ing relations : 
H (the magnetic force ) = 

4tt N I 
1( . j (Gilberts per cm.) 

<t> (the Aux)=mHA (Maxwells) 


B (the flux density )= -r (Gauss) 



M (the permeability ) = ^ T (numeric) 


Where : 

1 = Magnetic path in cms. 
A = Cross section in. cms. 
N = The number of turns. 
I = The current in amperes 
t = 3.1416. 

If we pass a gradually increasing 
current through a coil wound on a 
core of magnetic material the graph 
of the relation B/H takes the form of 
Fig. 1. 

If the current be now decreased to 
zero it will not retrace the original 
course but will follow the left-hand 
slope of the curve AE in Fig. 2. That 
is, for a given value of H there are 
three values of B corresponding to P 
in Fig. 1 and Q and R in Fig. 2. This 
is due to the residual magnetism in 
the core and the condition is known as 

If an alternating current be super- 
posed on the d-c. magnetizing current 
the resultant values of B and H will 
trace out a minor loop of more or less 
inclination to the B/H curve as shown 
in Fig. 3. where A B and A H are the 
increments of B and H respectively as 
arising from the superposed a-c. and 
/ " ac "AH 
which is the value of M employed in 

the design of audio-frequency trans- 

It will be seen that the value of 
^ ac is something quite different in 
arithmetic value than that obtained 
from the slope of the B/H curve. 
More elaborate delineations are given 
in the papers cited in the bibliography 
and they should be consulted by those 
interested in the experimental de- 
termination of the values. Adequate 
design data must be obtained from the 
curves issued by the manufacturers of 
core materials. 

In Figs. 4 and 5 are curves showing 
the a-c. permeability as against the 
a-c. flux density for several values of 
d-c. magnetizing force and the d-c. 
magnetization curve for a high per- 
meability core material, similar to 
Permalloy. These curves are accurate 
for the material over the range of 
d-c. values covered but are incomplete 
for purposes of design. 

The inductance of a primary winding 
is now 

L = 

4 7T A NV a 


the value of which may be readily de- 
termined from the available data. The 
complete curves may be obtained from 
the various core materials makers and 
a choice of core material made. 

The Optimum Air Gap 

If the air gap be provided in a mag- 
netic core the d-c. flux density will 
fall off but the a-c. permeability will 
increase. For some value of air gap, 
that is. for some substitution of a ma- 
terial having unit permeability for a 
portion of the magnetic path, where 
the a-c. permeability will be at a 
maximum for the value of d-c. mag- 
netization employed. In most audio 
transformers a certain percentage of 
air gap is required unless the d-c. 
magnetizing force is at zero due to the 


Curves of the 
magnetic prop- 
erties of trans- 
former and im- 
pedance core 

II | Mill 








a 200 


Bo = 11,600 GAUSS' 



10 15 30 60 100 200 



Curves of a-c. permeability plotted 
against a-c. flux density. 

position of the transformer in the cir- 
cuit or through the use of a parallel 
feed arrangement. Though in a push- 
pull transformer the two d-c. com- 
ponents buck each other and are 
assumed to cancel, high values of a-c. 
are usually in evidence together with 
a degree of d-c. magnetizing force due 
to irregularities in the tubes. 

For air the flux density is numer- 
ically equal to the magnetizing force, 
or B = H and the permeability is 

The calculations for the best value 
of air gap for a given set of conditions 
is a bit too involved for our discussion 
but may be obtained from the papers 
cited herein. 

The advantages of a high permea- 
bility core material are self-evident. 
The required primary inductance may 
be obtained with fewer primary and 
secondary turns and consequently lower 
distributive capacitance and leakage 
reactance. A high ratio transformer 
may be evolved having approximately 
the same detrimental effects of 
capacitance and leakage reactance as 
a transformer of much lower ratio em- 
ploying silicon steel. Thus it may be 
seen that we can eliminate distortion 
due to falling off of the gain frequency 
characteristic at the low frequencies 
and eliminate high-frequency resonance 
points and consequent high-frequency 
cut-off within the useful range by the 
employment of a high permeability 
core material. 

Calculation of Distributive 

The distributive capacitance of a 
winding is composed of the additive 

Projection Engineering, November, 1929 

Page 27 




2 14.006 


w 10,000 

<s 8,000 

> 6.000 

£ 4.000 

° 2,000 


1.0 2.0 3.0 4.0 



Another curve of a-c. permeability 
plotted against a-c flux density. 

layer-to-layer capacitances and the 
turn-to-turn capacitances. In multi- 
turn windings where the number of 
turns is large compared with the 
number of layers the latter may be 
neglected. Then, 


L = the length of the winding in 

1 = mean length of turn in cms. 

T = thickness of interleaving in cms. 

t = thickness of wire insulation. 

K = a constant equal to 22 x 10-14 
for paraffin paper. 

Calculation of the Leakage 

The primary and secondary leakage 
inductances are calculable from the 



8 + 

d, +d 2 


lO 8 henrys 

and referring to Fig. 6. 

r = mean radius of primary and 
secondary in inches. 

S = spacing between primary and 
secondary windings in inches. 

t = thickness of primary. 

t = thickness of secondary. 

n = primary or secondary turns. 

L = length of winding. 

These values correspond to the pri- 
mary and secondary leakage induc- 
tances as described in the preliminary 
article of the series. 

Methods of Winding 

There are many methods of winding 
calculated to lower the distributive 
capacity and the leakage inductances 
of the windings. One transformer 
design cited in recent literature was 
of a very cheap material as to core 
material and general construction. 

Koehler has shown a method of 
lowering the resonance peak of a trans- 
former by winding a proportion of 
resistance wire into the secondary. 
The particular transformer in question 
was wound in such a manner that the 
turns in the layers bunched up during 
the winding process automatically 
short circuiting a number of turns in 
each layer. The resistance introduced 

into the circuit by this means was 
sufficient to lower the resonance peak 
due to an otherwise poor design. 

Resistance windings are not the only 
solution, as was demonstrated in the 
last equation given in the first part of 
the series. There it was shown that 
resonance effects may be avoided by 
three methods ; i. e., by placing the 
resonance point beyond the useful 
range of the amplifier, by increasing 
the load resistance, or by having a 
high ratio of C to L in the resonant 

The revision downward of the reso- 
nance peak of the transformer shown 
in Fig. 11 of the previous article was 
by increasing the coil capacitance by 
increasing the length of the winding. 
There was a slight loss in inductance 
through the increased reluctance of the 
iron path and a consequent falling off 
at the lower frequencies. This could 
have been compensated by increasing 
the height of the stack. 

Koehler gives two methods of wind- 
ing by which the leakage inductance 
or the coil capacitance may be mini- 
mized and these may be studied by 




■ r P - 


FIG. 6 

Drawing of the cross-section of a 

transformer, indicating the core 

and the primary and secondary 


reference to his paper. Probably the 
most effective method of lowering the 
leakage inductances and coil capaci- 
tances is through the use of a high 
permeability core material as the ex- 
pense of involved forms of winding 
would entirely offset the saving to be 
had through the use of an inexpensive 

Distortion Other Than That of the 
Frequency Characteristic 

So far no mention has been made of 
distortion due to hysterisis or to the 
production of odd and even harmonics 
in the amplifier circuits. In Fig. 7 are 
shown the magnetization curves for 
two iron cores. One, curve A, contain- 
ing a small air gap in a comparatively 
small core and the other, curve B, 
representing a larger amount of iron 
with no air gap. A smaller core with- 

The magnetization curves of two 
iron cores. 

out the air gap would have assumed 
the curve represented by the dotted 
line. The d-c. magnetization current, 
represented by the abscissa o-c, has 
been correctly adjusted so as to be at 
a point half way between the origin 
and the saturation point. With an 
impressed signal, an alternating cur- 
rent represented by the cycle c-a-c-b-c 
is superposed in either curve the im- 
pressed current variations give rise to 
a proportional change in flux. Had the 
current been so adjusted as to allow 
the variations to overshoot the satura- 
tion point as in the case represented 
by the dotted line, the flux changes 
would have been non-proportional ana 
the distortion which would occur is 
obvious. Of course, the delineation 
given takes no account of hysterisis. 
Assume a magnetization curve as indi- 
cated in Fig. 8, where the hysterisis 
loop and the impressed sine wave are 
shown. The flux variation assumes 
the cycle c'-a'-c'-b'-c', corresponding to 
current variation over the cycle 
c-a-c-b-c and the resulting distortion 
of the wave form is shown in the 
figure. It can be seen that the smaller 
the hysterisis loop the nearer the wave- 
form of the output will resemble that 
of the impressed signal. The wave- 
forms may be readily compared on a 
cathode-ray oscillograph. 

Distortion in the Vacuum Tube 

It is hard to set a criterion for dis- 
tortion in an audio amplifying circuit. 
So much has been said regarding the 
physiological and psychological aspects 
of the case. So much has been said of 
drumminess — of excessive brilliance 
and so much regarding the technical 
aspects of matching the amplifier 
response to the response characteristic 
of the reproducer and of the associated 
circuits in general. The trend of these 
articles has been always toward the 

M a g n etization 
curve showing 
hysterisis loop 
and impressed 
sine wave. 


a 1 ^ 

i i i .i i -i i . i i 


' I T 3-1 2TT 5J 37r TJ 4T 
2 2 2 a 

FIG. 8 

Page 28 

Projection Engineering, November, 1929 

ideal in the amplifier circuit itself, 
with the hope that the associated 
equipment may at some future time be 
likewise idealized. 

In a thermionic vacuum tube it is 
known that the characteristic curve is 
not entirely straight along the working 
portion and that some distortion of the 
output due to the production of odd 
and even harmonics of the input fre- 
quency will result. It is not within 
the scope of this article to consider the 
mathematics of the case and it will 
suffice to say that if the grid circuit is 
not allowed to draw a current in excess 
of 10 ma. — that is, if thoroughly 
evacuated tubes be employed, and if 
in no instance is the grid allowed to 
become less than one volt negative, the 
production of harmonics will be limited 
in the vacuum tube itself to that due 

Fundamental and reversed windinc 
push-pull amplifier circuits. 

to the non-linearity of the working 
portion of the characteristic and on 
the resistance of the load. 

The push-pull amplifier has long 
been known for its ability to handle 
large power outputs without distortion. 
The fundamental circuit of the final 
stage is shown in Fig. 9-A. If an 
alternating current be impressed upon 
the primary of the input transformer 
the secondary windings in the push- 
pull stage are bucking each other and 
the a-c. components on the grids of the 
two tubes will be 180 degrees out of 
phase. But the second harmonic com- 
ponents (the double frequency term), 
going through one complete cycle for 
each half cycle of the fundamental will 
be 360 degrees out of phase in the two 
plate circuits, which is equivalent to 
their being in phase with each other — 
and if the two plate windings are con- 
nected so as to buck each other, as in 
Fig. 9-B, the harmonic voltages will 
balance out, while the two funda- 
mentals will be additive and constitute 
the output voltage. In this connec- 
tion it is interesting to note that if the 
plate windings are connected so as to 
aid one another the fundamental will 
cancel out and the tube circuit will 
act as a harmonic amplifier or fre- 

Special vacuum- 
tube voltmeter 
circuit for test- 
ing interstage 
coupling d e - 

.25 MR 


.01 MFT 

2 MEG. 



90 V. 

FIG. 10 


10,000 co 


quency doubler. This principle is em- 
ployed in high-frequency transmission 
for amplifying the output of a crystal 

Testing of Interstage Coupling 

It was previously stated that the 
capacitance affecting the resonance 
point and the high-frequency cut-off 
was the distributive capacitance of the 
secondary winding plus the effective 
input capacitance of the succeeding 
tube. In making measurements of a 
coupling transformer it is essential 
that all the conditions of actual ser- 
vice be fulfilled during the run. The 
average vacuum tube voltmeter circuit 
does not meet the requirements and 
some arrangement must be made so as 
to have the measuring instrument 
present to the device the same con- 
ditions as an actual succeeding stage 
of amplification. It is also necessary 
to allow for any variation of the indi- 
cating device with frequency. 

The input to the vacuum tube in the 
amplifying circuit is from a beat — fre- 
quency oscillator and the input voltage 
is measured by a thermo-couple and 
microammeter — the voltage being 
equivalent to the resistance across 
which the voltage is taken multiplied 
by the indicated current. The volt- 
meter is as shown in Fig. 10, and em- 
ploys two -27 tubes in series with 
their filaments heated by a storage 
battery. The meter may be calibrated 
at the higher frequencies by means of 
the thermo-couple and resistance box. 

Many methods of measurement for 
inductance coils which carry d-c. have 
been evolved and more or less accuracy 
is possible from all of them. The 

writer has employed for some time 
past the setup shown in Fig. 11. 

Referring to the figure, the a-c. volt- 
age is applied across a transformer 
designed to give voltage ratios of 
20/1, 5/1, 1/1, and % by means of the 
tap switch shown. The fine adjustment 
is by means of the potentiometer Rj. 
The a-c. voltage is in series with a 
standard resistance R 3 and the parallel 
arrangement of the sample under 
measurement and the standard reactors 
L x and L 2 . By means of S x the v.t. 
voltmeter is switched from across R 3 
to the sample. The d-c. is taken across 
the resistance R 2 which is a slide wire, 
and is measured by means of the 
milliammeter (I d-c). The two con- 
densers Ci and C 2 block the d-c. out of 
the a-c. circuit. L 3 and C 3 are a filter 
circuit to keep commutator ripple and 
stray a-c. from entering the circuit but 
L 3 may be shorted out at large cur- 
rents where its resistance might be 
appreciable. Sj is a switch employed 
to throw L, or L 2 into the standard 
position according to the value of the 
d-c. employed. The v.t. voltmeter used 
to measure the voltage across the 
standard resistor and the sample must 
be of high input impedance as the 
resistances involved are of the order 
of several hundred thousand ohms. 

The operating procedure is as fol- 
lows : The switch Si is set for a con- 
venient value of a-c. and R 3 varied 
until a balance is obtained when the 
voltmeter switch is moved from side 
to side. Adjustment of the potentio- 
meter is made so that the voltmeter 
shows the voltage at balance at which 
the sample is to be tested. The ap- 

(Continued on page 35) 

C1-.25ME C3 = .25MF 

C2 = .50 MF. 

L1 = 60 HENRY, 100 MA. L2 = 320 HENRY, 
L3 = 60 HENRY, 100 MA. 30 MA. 

R1,R2 = 2000 OHM SLIDE WIRE 

110 V. 












^£QQ0_> — ' 

" 1 1 


Circuit for the measurement of inductances which carry direct current. 

Projection Engineering, November, 1929 

Page 29 

A Few Facts About Filters 

Special Type Filters for Use in Power Supply Circuits 
By John F. Rider, Associate Editor 

FAITHFUL reproduction necessi- 
tates rigid control of the fre- 
quencies present and being 
passed through the amplifying 
system. Albeit the fact that the nor- 
mal audio band is quite broad and that 
acoustics in theatres play a paramount 
role, it is still necessary to impose cer- 
tain limitations upon the action of the 
circuits in an amplifier and its asso- 
ciated equipment. Very little c ran- 
plaint can be registered about the con- 
ventional filter system employed in 
rectified a-c. sources of plate and grid 
potential for the amplifiers employed 

Generalized circuit structure of a 
7r-type wave filter. 

in a talkie installation. Yet we find 
that the hum level is appreciable in 
many such installations, particularly 
when the amplifier is opened wide. 
Now hum, be it with a fundamental of 
60 cycles or 120 cycles, is not only a 
source of disturbance because of the 
fact that it is audible, but it interferes 
with reproduction, combined with 
regular speech frequency to accentuate 
or attenuate depending upon the in- 
stantaneous phase relation. 

Much has been said about the use 
of push-pull systems as a means of 
eliminating hum voltages because of 
the characteristics of the system. Yet 
we find that the use of push-pull sys- 
tems does not mitigate the effects of 
poor filtering in a rectifier system. 
With respect to the filters, the average 
system is based upon conventional 
design involving the "tank effect" of 
the input condenser (nearest the recti- 
fier) and with very little attention paid 
to the type of load (impedance) or the 
actual characteristic of the system 
when in operation. The criterion is the 
actual performance of the amplifier- 
rectifier combination. While the gen- 
eral performance is satisfactory, we 
doubt if the magnitude of hum voltage 
present in the average a-c. system 
would be permitted to exist if it were 
due to some form of coupling when all 
voltages were d-c. 

Filter Chokes 

It must be admitted that all of the 
hum in the system is not due to the 

rectifier filter, but whatever reduction 
can be effected in the filter system, just 
that much improvement is secured. 
We shall not attempt a complete 
analysis of filters in these pages. In- 
stead we shall give a few practical 
examples of filter structure which have 
proved themselves in practice. It 
might be of interest to mention at this 
time, that the elements employed in 
the filters designed according to the 
formulae mentioned in these pages 
were of special construction and much 
larger than the ordinary elements em- 
ployed in everyday practice. The in- 
creased cost was found worthwhile and 
the special construction justified the 
expense. In addition it might be well 
to mention that the greatest difference 
was encountered in the action of the 
filter chokes normally employed and 
those specially constructed, when d-c. 
was caused to flow through the wind- 
ings. The units specially constructed 
were made after the values were calcu- 
lated and were of such design that the 
variation in inductance was not in 
excess of 15% when the load current 
was increased from 50 to 150 ma. The 
total difference between and 150 ma. 
was less than 20%. On the other hand 
chokes of conventional types tested in 
practice showed variations as great as 
60% in inductance when the load was 
increased from a very small value of 
direct current to the rated value. In 
one extreme case a choke rated at 30 
henrys and 100 ma. was found to 
possess an inductance value of exactly 
7 henrys with 100 ma. of direct current 
flowing through the winding. The sig- 
nificance of this variation will be 
realized when we consider the cutoff 
frequency of the filter. 

The Wave Filter 

The function of a wave filter is to 
separate current waves of different fre- 
quency. The specific design governs 
the action. It can be arranged to pass 
all frequencies below a certain cutoff 
frequency ; all frequencies above a 
cutoff frequency ; all frequencies be- 

tween two cutoff frequencies and to 
eliminate all frequencies between two 
cutoff frequencies. Designation of 
these four forms of filters are respect- 
ively, L.P. or low-pass ; H.P. or high 
pass, B.P. or band pass and B.E. or 
band ejector. It is the purpose of this 
article to describe the low-pass and 
the band-pass types of filters. How- 
ever, space does not permit a full 
resume of all of the forms of filters 
which perform in this manner, hence 
we select the most popular systems. 

Recognition of the purpose of a 
power-supply unit and the requisite of 
no a-c. component in the d-c. output 
signifies that we require a low-pass 
filter with a theoretical cutoff at zero 
frequency. The output of the rectifier 
tube or element contains a funda- 
mental harmonic of a value governed 
by the type of rectification employed 
and the frequency of the input line 
voltage. If the system is half-wave, 
the fundamental frequency present in 
the filter is of the value equal to the 
input voltage frequency. In addition 
to this frequency component in the 
pulsating output we have higher mar- 
monies of decreasing amplitude. If the 
system is full wave, the fundamental 
is equal to twice the input voltage fre- 
quency and we again have higher har- 
monics of diminishing amplitude. Since 
the conventional arrangements are 
actually of two types, employing both 
half -wave and full-wave rectification 
it will be necessary to consider both. 
Hence the fundamental frequency 
found in the rectified output is 60 
cycles when the input voltage frequency 
is 60 cycles and a half -wave rectifier 
is employed and 120 cycles when the 
system is full wave and the input 
voltage frequency is likewise 60 cycles. 
Generally speaking the important fre- 
quencies found in the rectifier output, 
judging by the characteristics of an 
ideal rectifier with respect to relative 
amplitude of the a-c. components and 
the magnitude of the d-c. output, are 
the fundamental, second and fourth 
harmonics. Expressed numerically, if 
the input is 60 cycles and the system 

A 7r-tyoe fi'te- 
circuit and 
curve showing 
its frequency 
a t ten uation 






r-' 0000 ^-i 





< j > / 

C _ 
2 " 


C . 
2 " 

- R r 1 

) Fc 



FIG. 2 


Page 30 

Projection Engineering, November, 1929 


L L 

YTflftflPi I i^ffioTV 




C=4C 1 (a 2 -0 

4TTFcRaVa 2 --l 

L=R 2 C 
F M 



Another low-pass, Tr-type filter cir- 
cuit and curve showing its fre- 
quency attenuation characteristics. 

is half-wave, these values would be 
60,120 and 240 cycles. 

Reference to Figs. 2 and 3 illustrates 
two filter structures with their respect- 
ive attenuation characteristics. The 
filter circuit structure i n pig. 2 will 
be found identical to the systems now 
in use, whereas that shown in Fig. 3 
differs in but few respects. The curves 
show degree of attenuation. Consider- 
ing Fc as the cutoff frequency, it is 
evident that the systems are both low- 
pass filters, since they pass all fre- 
quencies between O and Fc and attenu- 
ate all frequencies higher than Fc. 
With respect to the attenuation 
characteristics, it is evident that they 
are not the same in both cases. In 
the first, Fig. 2, the maximum attenu- 
ation takes place at an infinite fre- 
quency, the degree of attenuation in- 
creasing as the frequency above Fc is 
increased. Albeit the fact that this 
type of filter is most prevalent, it be- 
comes obvious that it is not the ideal 
filter for use in a rectifier circuit, since 
the magnitude of the amplitude of the 
harmonics present in the output of the 
rectifier does not follow in line with 
the characteristic of the filter. In 
order that the filter be most effective, 
it would be necessary that the higher 
harmonics be larger in amplitude than 
the fundamental and the next two or 
three harmonics. As it happens this is 
not the case. The fundamental is the 
strongest with diminishing amplitude 
upon the succeeding harmonics. Of 
course it is possible to set the cutoff 
frequency very low, say at 10 cycles for 
either the 60 or the 120 cycle funda- 
mental, and thus secure best operation, 
but even then the degree of attenuation 
on the strongest frequency, the funda- 
mental, would not be as great as the 
attenuation of the harmonics, despite 
the fact that just the contrary is de- 
sired, since the fundamental is several 
times as strong as the nearest har- 

Degree of Attenuation 

Reference to the characteristic of 
Fig. 3, shows that this type of circuit 
structure would be ideal. Here we 
find a distinct difference in operation. 
Our cutoff frequency Fc is available 
but infinite attenuation (theoretic- 
ally) is available at a finite frequency 
Fm, with lower attenuation on higher 
frequencies. If we strive for infinite 
attenuation at the fundamental fre- 
quency, making that value Fm equal to 
either the 60 or the 120 cycle voltage, 
depending upon the frequency of the 
line supply and the type of rectification 
employed, we secure maximum attenu- 
ation at the desired point. Inci- 
dentally, if the line supply is 50 cycles, 
the fundamental in a half -wave system 
would be 50 cycles, and in a full-wave 
system it would be 100 cycles. With 
25-cycle input, the fundamental in a 
half-wave system would be 25 cycles 
and in a full-wave, would be 50 cycles. 
We shall devote our efforts to a 60- 
cycle input with full-wave rectification. 

With respect to the difference in 
circuit structure and attenuation, we 
find that the point Fm is due to the 
presence of the parallel resonant cir- 
cuit LCI (Fig. 3). Recognizing that 
one of the frequencies present in the 
a-c. component of the rectified output 
is very much stronger than the re- 
mainder, infinite attenuation at that 
frequency should be of great aid. It 
might be of interest to state that the 
desired condition is attained in 

Filters in general are artificial links 
between two power circuits, a source 
of power and an absorber of power. 
Consequently the impedance relation 
between the source of and the absorber 
of power and the filter circuit must be 
of specific nature, of like value. In 
other words, the impedance of the 
filter must match the two image im- 
pedances. We can definitely decide 
upon one of the image impedances, the 
load, being the function of the voltage 
and current output of the complete 
filter. The other, the rectifier, is ex- 
ceedingly complex, the internal im- 
pedance being a complex function of 
the current flowing through the recti- 
fier. Fortunately it may be neglected, 
a fact proved in practice. 

The two filter structures shown in 
Figs. 2 and 3 are of the T-type repre- 
sented in Fig. 1. Here we find Zl to 
be the series element and Z2 to be 
the two shunt elements. In a ""-type 
of filter the terminating impedances 
always have twice the impedance de- 
termined by formulae, as indicated by 
2Z2 either side of Zl. We show Zi in 
series with a source of voltage as a 
simple example of the application of 
the filter, although Zi associated with 
E is not the true representation of the 
impedance of the rectifier tube. 

Let us consider the application of 
the structures shown in Figs. 2 and 3 
to a typical rectifier. The rectifier unit 
complete is designed to supply 450 
volts at 150 ma. This value of current 

includes the total drain and the 
bleeder current. Hence the amplifier 
circuit (the load), has a resistance of 
450 h- .150 or 3000 ohms. The system 
of rectification is full-wave employing 
two 381s. The input frequency is 60 
cycles ; hence the fundamental in the 
output is 120 cycles. Applying Fig. 2, 
we must select a cutoff frequency 
which will afford satisfactory attenua- 
tion at 120 cycles. Twenty-five cycles 
is far enough away from 120 to provide 
satisfactory operation. Hence the value 
of L will be according to the formula 


L in henrys 

3.1416 x Fc 



L = = 38.2 henrys. 

3.14 x 25 

C in farads 

3.1416 x Fc x R 


C = 

3.14 x 25 x 3000 mf . 

=.00000425 = 4.25 

The two terminating impedances 
must be twice the value determined in 
the formula, hence C -=- 2 would be 
2.13 mf. for the input and the output 
condensers in the two-section filter 
shown. The requirements for such con- 
densers when based upon voltage regu- 
lation and tank effect, allow the use of 
2 mf. for the input condenser but 
recommend a higher value of capacity 
for the output condenser. While the 
2 mf. unit operates in a satisfactory 
manner it is possible to increase the 
value to 4 mf. without interfering to 
a very large extent with the operation 
of the filter. However, several com- 
mercial filters employ a 2 mf. output 
condenser and the results are normal. 
Comment is necessary relative to the 
inductance value of the chokes. The 
number of henrys determined by 
means of the formula must exist when 
the full load of 150 ma. is flowing 
through the chokes. As is evident, the 
current flow and the voltage and cur- 
rent requirements of the filter are im- 
portant with respect to the constants. 

The first rectifier is suitable for use 
with type — 50 tubes and associated 
amplifiers. Suppose we select the con- 
stants for another filter which is to 
operate in conjunction with a rectifier 
designed for — 45-type tubes to supply 
250 volts at 90 ma. The resistance R 





- c 

C _ 


-'£' •■ 



C 2 







Fig. 4. The same filter arrange- 
ment shown in Fig. 2, indicating 
its connection between the load 
and the source of power. 

Projection Engineering, November, 1929 

Page 31 

is therefore 250-^.090 = 2780 ohms. 
Applying formula ( 1 ) we have 

L = = 35.4 henrys. 

3.14 x 25 

3.14 x 25 x 2780 

=.0000045S = 4.58 
mf. (2) 

The input and output condensers are 
C -*- 2, hence, 2.29 mf. With respect 
to the fractional values, close tolerance 
is not required, a 2.25 mf. unit being 
satisfactory in place of the 2.29 mf. 
and a 4.5 mf. condenser being satis- 
factory in place of the 4.59 mf. unit. 
So much for the application of the 
simple filter shown in Fig. 2 for use in 
rectifier systems. In the event that the 
cutoff frequency is desired the follow- 
ing may be applied 

Fe = 

3.14 x.V LxC 

where L is in henrys and C in farads 
Let us now apply the system shown in 
Fig. 3 and develop the various con- 
stants. Once again the terminating 
impedances are twice the value deter- 
mined in the formula. We now must 
decide upon two frequencies in addi- 
tion to the load impedance. We shall 
consider the impedance values pre- 
viously used and employ 120 cycles as 
the value at which we desire maxi- 
mum attenuation. This frequency 
shall be denoted as Fm. In order to 
simplify matters we shall make Fc 
equal to 30 cycles. The separation is 

L in henrys = R 2 C 

CI in farads 


4 t Fc R a V a 2 — 1 

C in farads =4C1 (a 2 — 1) (6) 


where a = in this case = 



= 4 



Fig. 5. The same filter arrange- 
ment shown in Fig. 3, indicating 
its connection between the load 
and the source of power. 

secure the values of L and C. Sub- 
stituting into formula 5 we have for 
the 3000-ohm load 


12.56 x 30 x 3000 x 4 x 3.87 

We must solve for CI in order that we 



CI = .0000000572 F = .0572 mf. 

According to formula (6) 

C = 4 x .0000000572 x 15 

C = .000003432 F = 3.43 mf . 

The value of L in henrys is according 
to formula (4) 

L = 3000 2 x .00000343 

L = 30.87 henrys 

The terminating impedances are 
twice the values calculated or C -=- 2 = 
1.265 mf. With respect to the input 
capacity of approximately 1.25 mf. in- 
stead of the conventional 2 mf., the 
actual difference in voltage was found 
to be about 33 volts in a system de- 
signed to supply 450 volts. With re- 
spect to the output condenser in the 
two-section filter it is possible to use 
higher values, because this capacity in 
connection with L CI governs the 
value of Fc for that single section. 
It is true that this is not exactly ac- 
cording to Hoyle in so far as filter 
design is concerned, but it works out 
well in practice. Hence the output 
condenser instead of being 1.265 mf. 

can be about 4 mf. The input con- 
denser should remain the value desig- 
nated, namely, 1.265 mf., because the 
use of a low value of capacity reduces 
the load upon the rectifier tube. The 
mid-section condenser is the calculated 
value, 3.43 mf. 

In the event that the cutoff and 
maximum attenuation frequencies are 
desired, the following formulas are 
submitted : 

Fc = 

3.1416 V Llx (C +4C1) 




6.28 V L1C1 

Other Applications 

Recognizing that these filters are 
low-pass filters, their application is 
not limited to a-c. sources of d-c. po- 
tential. They are equally suitable for 
use in the output circuit of the power 
tubes between the tubes and the 
speakers, where it is desired to pass all 
frequencies below a certain cutoff fre- 
quency. It is equally suitable for use 
in pickup circuits where the system 
shown in Fig. 3 could be well utilized 
to provide maximum attenuation on 
the scratch frequency, if a certain fre- 
quency value can be decided upon as 
representative of this disturbance. 
The structure used in Fig. 2 can be 
applied between a detector tube and 
the input amplifier unit when a radio 
receiver is utilized as the source of 
music being transmitted through a 
number of channels in a hotel or apart- 
ment house. Incidentally this system 
is actually in use in several commer- 
cial receivers of high calibre. 

Two such filters are shown in Figs. 
4 and 5. These two are suitable for 
application to the conventional tube 
rectifiers employed in quite a large 
number of talking motion-picture in- 
stallations. Although we do not make 
specific mention, the type of filter 
shown in Fig. 5 is suitable for appli- 
cation to the suggested rectifier sup- 
plying 250 volts at 90 ma. as well as 
the unit which is quoted as being de- 
signed to supply 450 volts at 150 ma. 


(Continued from page 25) 

Crabtree, president elect, Society of 
Motion Picture Engineers, Colonel John 
A. Cooper, president, Motion Picture 
Distributors and Exhibitors of Canada. 

After the banquet the entertainment 
was provided by courtesy of the 
Famous Players Canadian Corporation, 
Ltd., with a Publix unit, under the 
direction of Jack Arthur. The Society 
received many courtesies through the 
splendid co-operation of the Ontario 
Government and the theatres of 

Credit should be given to the Con- 
vention or Arrangement Committee, 
headed by W. C. Kunzman, chairman, 
and the remainder of the Committee, 

W. C. Hubbard, H. T. Cowling, G. E. 
Patton, M. W. Palmer, B. E. Norrish, 
Wm. Redpath, F. C. Badgley, H. N. 
DeWitt, all deserve the sincere 
appreciation of the entire motion- 
picture industry. 


(Continued from page 15) 

desired. During the first scene and 
in the interval between it and the fol- 
lowing scene, the lighting effects for 
the subsequent scene will be preset at 
the modulators by the lighting oper- 
ator and, when the change occurs, the 
first group of modulators will be dis- 
connected from the circuit and the 
second connected in the circuit simply 
by a flick of the master tumbler 

switch, when operation will proceed as 

To Use Periscope 

The lighting operator and his con- 
trol devices will be located, in the Chi- 
cago Civic Opera House, in a booth 
similar to and near the prompter's 
booth, enabling him to see all the light- 
ing on the stage, and a periscope 
through which he can see all the light- 
ing in the auditorium proper. All the 
selsyns and modulators will also be lo- 
cated at this point, but will occupy 
very little room as they are compactly 
built. The reactors will be mounted 
on frames at remote points where 
there is room, such as beneath the 
stage or on the "grid" level high above 
the flies. The wiring to the lights will 
be arranged as heretofore. 

Page 32 

Projection Engineering, November, 1929 

The Portable Model RCA Photophone 

Description of the New 35 mm. Equipment Which Includes a Portable 
Screen, Projector and Power Amplifier 

By H. L. Danson 

THE first sound motion-picture 
equipment company to definitely 
announce its entry into the edu- 
cational and industrial sound- 
film field is RCA Photophone. Not only 
is that company in a position to pro- 
vide recording facilities to anyone de- 
siring to produce educational and in- 
dustrial films, but RCA Photophone, 
going beyond any optimistic forecasts 
and vaguely defined plans, now has on 
the market a readily portable sound- 
picture projection equipment which 
will revolutionize education and adver- 

This portable equipment was origi- 
nally conceived by RCA Photophone 
and its affiliates, the Radio Corpora- 
tion of America, General Electric Com- 
pany, and Westinghouse Electric and 
Manufacturing Company, to provide a 
transportable apparatus for sound-on- 
film reproduction at banquets, conven- 
tions, conferences, etc. The extreme 
adaptability of the device to educa- 
tional purposes and the advertising- 
craft, was revealed when it was pro- 
posed that RCA photophone record a 
number of lecture talks on standard 
35-mm. film of famous explorers, 
scientists and public men. 

This equipment is now a reality. It 
has been demonstrated publicly and 
has thoroughly indicated its extremely 
practical portability. But essentially 
this new Photophone development is a 
sound-projection machine, and on its 
merits as a faithful reproducer, it has 
convinced the most skeptical of its cap- 
able performance. 

In purpose, as outlined by E. E. 
Bucher, executive vice-president of 
RCA Photophone, the new portable 
system is intended for universities, col- 
leges, schools, churches, hospitals, wel- 

An RCA Photophone portable projector for sound and picture, dismantled 
and ready to be packed in its small trunk. At the left of the projector cas- 
ing, in the trunk, are the legs and frame of the support for the machine. 
The magazines are shown at the extreme left and right of the illustration. 

fare institutions, clubs, commercial or- 
ganizations and similar groups that are 
now finding the talking screen the ideal 
medium for transmitting information. 

Recording Facilities 

Previous announcements of this new 
RCA Photophone development have 
linked it with the recording facilities of 
that company at the Gramercy Studios 
in New York. These studios constitute 
a perfect sound motiompicture pro- 
ducing plant where all interested par- 
ties can make education, informative, 
advertising and industrial films, with 
the expert assistance of scenarists at 
the studios. Talking Picture Epics, Inc., 
an organization created to further the 
field of information on exploration and 

The amplifier 
for the sound- 
picture system. 
The power sup- 
ply and rectifier 
are included in 
this case. The 
volume control 
knob can be 
seen on top of 
the unit. 

natural history, is producing just such 
a series of film lectures at the Gra- 
mercy Studios, with George Palmer 
Putnam, Captain Bob Bartlett, Dr. 
William Beebe, Roy Chapman An- 
drews, and other equally celebrated ad- 
venturers and explorers for the Amer- 
ican Museum of Natural History, on 
the list. "The Girl Scout Trail," a 
Visugraphic production, which is being 
widely exhibited at girl scout clubs, 
theatres, women's leagues and similar 
organizations, is a similar type of 
synchronized film. 

But the field is virtually unlimited. 
The extraordinary facility with which 
the talking film lends itself to medical 
instruction can best be appreciated 
when it is understood that 50 students 
watching a surgeon can see little more 
than their eyes and the position of 
their seats permits them to see. On the 
film, closeups can carry the spectator 
to the heart of the operation ; but 
greater than that, the talking film 
gives the spectator a running lecture 
outlining in detail the elements of the 
surgery. Any form of instruction, lec- 
ture, public-address and informative 
discourse can be duplicated a thou- 
sand times in a thousand widely 
separated points by the use of the 
portable reproducing system. 

Engineering Details 

The engineering details of the new 
RCA Photophone portable sound and 
picture reproducing system are of ex- 
treme interest because of the identity 
between this equipment and the stand- 
ard large theatre reproducing appar- 
atus of Photophone installed in premier 
picture houses of the world. The first 

Projection Engineering, November, 1929 

Page 33 

consideration calls for the projection 
of standard 35-mm. film with sound 
track, such as is exhibited in theatres 
at the present time. This the device 
accommodates, reproducing the pic- 
ture through a picture-projection sys- 
tem of lenses affording a brilliantly 
lighted, sharply defined picture on the 
screen. At a throw of 50 feet, the 
standard lens supplied gives a picture 
six by eight feet in size. Other lenses 
are supplied at the purchaser's op- 
tions, providing pictures of various 
sizes at special "throw" distances, to 
accommodate all conditions. 

The reproduction of sound is accom- 
plished through the highly developed 
RCA Photophone optical system and 
pliotoelectric cell assembly employed 

The screen used with the portable 
Photophone system. This screen 
collapses into a small carrying 
trunk, the frame being made of 
stout pipe in telescopic construc- 
tion. The feet come off and are 
packed with the other elements of 
the screen. The screen proper is a 
sound transmitting screen; the 
loudspeaker is set up behind it. 

in theatre equipments. The film speed 
is the standard of 90 feet a minute, 
and the projector operates from a 
power source of 110 volts, 60 cycles, 
alternating current. 

The entire picture and sound pro- 
jection system is housed in an attrac- 
tively finished all-metal cabinet 24 
inches square and 12 inches in width, 
mounted on four adjustable legs of 
lightweight telescopic construction. 
All connection plugs are non-inter- 
changeable, preventing injury to the 
equipment through error in connect- 

The Amplifier 

The amplifier is housed in a metal 
cabinet of similar dimensions, 
equipped, as is the projector, with 
handles for carrying. Only one con- 
trol, a large, handily-placed volume 
control knob, is visible, recessed in the 
top of the amplifier cabinet. This 
volume control is of the improved type 
now used in RCA Photophone theatre 
installations and permits the excep- 
tionally fine adjustment of volume in 
graded steps of 2-db. from the zero 
point to maximum. Standard RCA 

Radiotron vacuum tubes, such as are 
utilized in all RCA Photophone equip- 
ments, step the photoelectric cell cur- 
rent to the value where it can operate 
the loudspeaker system. A supply of 
direct current is furnished through a 
system of rectifiers. 

One of the exclusive features of the 
system is accommodation in the ampli- 
fying apparatus for a second projector. 
This arrangement also provides a 
sound changeover switch, as in regu- 
lar theatre installations, for changing 
from one projector to another, there- 
by insuring a continuous performance 
without reel-changing intervals. 

RCA Photophone's new improved 
type of loudspeaker, the electrodyna- 
mic moving coil cone utilized as a 
driving unit for a directional baffle, is 
standard equipment with the portable 
system. The entire loudspeaker as- 
sembly collapses into a small trunk no 
larger than a salesman's carrying- 
case, providing ready portability of 
the unit. 

In all its details, the RCA Photo- 
phone portable is simple, as well as 
handsome in appearance. The few 
necessary power connections are made 
by unobstrusive cable lines. The equip- 
ment occupies negligible space in oper- 
ation, and (which is of greatest im- 

A two-projector unit, which pro- 
vides a continuous snowing. The 
amplifier is built to carry two pro- 
jectors and is equipped with a 
standard form of fade-over switch. 

portance) it takes less than 15 min- 
utes to assemble or dismantle the equip- 
ment. The many educators, welfare 
workers, club leaders and industrial- 
ists who witnessed the operation of 
this equipment at a public demonstra- 
tion recently in the RCA Photophone 
Modernistic theatre in New York City, 
were enthusiastic in their commenda- 
tion of the development of the device. 


UNTIL recently it was supposed 
that the paper cone of a loud- 
speaker acts as a unit, like 
the piston of an engine mov- 
ing at high speed and generating stand- 
ing waves in the air. To reproduce 
this function, a stiff, non-stretching, 
light material is required, hence the 
use of paper as cone material. Re- 
search by the engineering staff of the 

Stevens Manufacturing Corporation of 
Newark, N. J., however, has disclosed 
the fact that, except under very special 
conditions, the behavior of cones is 
very different. Instead of acting as a 
unit, the cone can set up air waves by 
at least five different motions and com- 
binations of motions. On the low fre- 
quencies, trough-like waves are formed 
from the apex outward, the ends of 
the curves tending to become sine 

'Mm driving side of the portable Photophone. Note the simple travel of the 
Im from the upper film magazine, through the picture projector mechanism, 
Dund reproducing mechanism and into the lower takeup magazine. The 
pposite side of the projector contains the drive shafts, gearing mechanism, 


Page 34 

Projection Engineering, November, 1929 

Standardized Sound Film Aperture 


Nation-tvide Survey Shows Theatres Are Using Wide Variety of 

Aperture Sizes 

HOLLYWOOD motion-picture 
studios are now composing 
all vital elements in sound-on- 
film pictures within an area 
of 0.620 by 0.835 inches although con- 
tinuing to photograph the whole frame. 
This is in accordance with specifica- 
tions recently recommended by the 
Academy of Motion Picture Arts and 
Sciences Technicians' Branch acting 
jointly with the Technical Bureau of 
the Association of Motion Picture Pro- 
ducers, the American Society of Cine- 
matographers, the Pacific Coast Sec- 
tion of the Society of Motion Picture 
Engineers and the California Chapter 
of the American Projection Society. 

Theatres which restore the full 
screen image from sound-on-film pic- 
tures have been notified that to secure 
the maximum image size in 3 by 4 pro- 
portion they should use projector 
apertures whose size would be 0.600 by 
0.800 inches on the basis of projection 
on the level, the horizontal center of 
the aperture coinciding with the hori- 
zontal center of the S. M. P. E. Stand- 
ard aperture. 

The recommendations and action by 
the studios followed the revelation 
through a nation-wide survey that 

theatres are using a wide variety of 
aperture sizes in projecting sound-on- 
film pictures. It was also found that 
an increasing number of theatres are 
restoring the full screen proportion 
through the use of a smaller aperture, 
lenses of one-half inch shorter focal 
length, and various recentering de- 
vices. As only two studios were com- 
posing to allow for this the result was 
that in many theatres part of the 
heads and feet of characters were cut 
off in projection. The recommenda- 
tions of the technical societies are 
designed to correct this serious con- 
dition and were chosen as the best 
means of the projector aperture sizes 
among a number of large theatre 

Studios which are now marking the 
ground glasses of their cameras to con- 
form to the recommended practice 
are: Paramount-Famous-Lasky, Metro- 
Goldwyn-Mayer, United Artists, Pathe 
Universal, R. K. O., Tiffany-Stahl, 
Mack Sennett, Darmour, Educational ; 
the Fox Studio markings are the same 
width but allow .04 inches more 

Committees representing the motion- 
picture technical organizations in 

Restoration of Aperture to 3 
x 4 Proportion on Basis of 
Dimensions Recommended 
by Academy of Motion 
Picture Arts and Sciences. 

Circle Represents 3 
Head Close-up. 

A-Original "B and H" Silent 
Aperture— .720"x9375". 

B-A with Sound Track— .085". 

C— Recentering of B — 

— Account of Sound Track. 

D-C Recentered — with Camera 
Aperture as shown — .620'' x 

E-Head Reduced to meet projec- 
tion requirements of Proj. 
Aperture in F. 

F— New Proj. Aperture, size .600" 
x .800", inside Camera Aper- 
ture showing Head reduction. 

G and H represent cutting of 
Head in Projector by im- 
proper Framing. 

Hollywood are also studying the prob- 
lems of standard release print practice 
and screen illumination under the 
sponsorship of the Academy. 

(By V. E. Miller, Paramount-Famous-Lasky) 
In caption "A" above, there should be a decimal before the numbers "9375." 


(Continued- from page 21) 
its absorption in such a surface, make 
itself apparent to the sense of touch. 

Revolving Microphone 

The room is equipped with a loud- 
speaker and microphone but devoid of 
other furnishings. To assure accuracy 
in tests, the microphone used to pick 
up sound from the speaker is mounted 
on an arm four feet long which re- 
volves at the rate of approximately 
twenty revolutions per minute. 

The primary reason for revolving 
the microphone is to average the varia- 
tions in sound pressure which are the 
result of unavoidable reflection. It 
would be unnecessary to move the 
microphone at all if reflection were 
completely eliminated. The high ab- 
sorption and random reflection of the 
room serves merely to reduce the 
magnitude range of the sound pressure 
variations to limits which are within 
the ability of the measuring instru- 
ments to handle ; otherwise these in- 
struments would not read the true 
average of the pressures encountered 
by the microphone around its path of 

The testing apparatus outside the 
room consists of an audio oscillator or 
frequency machine which supplies the 
signal to the loudspeaker and resist- 
ance-coupled laboratory amplifier the 
input of which is connected to the 
microphone and the output to the 
thermo-couple microammeter. 

The loudspeaker and microphone 
may be considered merely as a con- 
necting link between the oscillator, or 
source of electrical energy, and the 
amplifier meter system, or indicator of 
electrical energy. Electrical energy is 
converted into sound by the loud- 
speaker and back again into electrical 
energy by the microphone. Due to the 
characteristics of the loudspeaker, the 
efficiency of conversion varies with 
frequency, causing different amounts 
of electrical energy to be indicated by 
the meter. At each frequency, an ad- 
justable electrical network capable of 
producing definitely known losses is 
substituted for the loudspeaker-micro- 
phone portion of the system and is 
adjusted until the same reading of the 
meter is .obtained as was given by the 
loudspeaker. Then, the setting of this 
electrical network, as read from its 
dials, is a measure of the efficiency of 
the loudspeaker at the frequency under 

Projection Engineering, November, 1929 

Page 35 

The Photoelectric Cell 

Light Energy and the Photoelectric Effect 

THE most common forms of en- 
ergy are mechanical energy, 
heat, chemical, electrical, mag- 
netic, sound and light energy. 
Some of the things we wish to do 
with these forms of energy are, to 
capture them from their natural 
sources, to store, transport, transmit, 
measure, record, observe, control, 
transform them into other forms of 
energy, and to control one form of 
energy by another. For example, me- 
chanical energy exists in the form of 
water flowing in streams. We capture 
this from nature by hydraulic tur- 
bines. We store this by holding the 
water at an elevation in reservoirs. 
Mechanical energy is carried in stor- 
age by everyone who has a watch. 

The effects of mechanical energy are 
common to observation. Its control is 
commonly by clutches, brakes, etc., and 
it controls other forms of energy by 
means of electrical contacts, triggers 
on guns, etc. That is to say, a small 
amount of mechanical energy applied 
to the trigger of a rifle controls a large 
amount of chemical energy. A similar 
story might be written about other 
forms of natural energy. But when 
we come to energy in the form of light, 
we find that the story is rather brief 
in spite of the fact that light energy 
is perhaps one of the most important 
to the human race. 

Light Energy 

Light energy is captured from na- 
ture almost solely by plant growth. 
To store it, except in minute amounts 
by phosphorescent chemicals, is impos- 
sible. Since it cannot be stored, it 
cannot be transported in storage. It 
transmits itself, but its measurement 
is a thing of considerable difficulty, 
and recording is even more difficult. 
To control its formation from other 
forms of energy is usually relatively 
easy, but for it to control any other 
form of energy is very difficult. Its 
transformation into other forms of 
energy is greatly limited by lack of 
suitable means. 

In this discussion of light, we must 
not forget that light, as ordinarily ac- 
cepted, is distinct from radiant heat, 
and hence the energy as light is really 
quite small. If heat be absorbed out 
of sunlight, the remainder is a very 
small amount of energy. This energy 
cannot be transformed into usable me- 
chanical energy. It may be trans- 
formed into heat, but the resulting 
heat is very small. It is transformed 
into chemical energy by many natural 
processes of growing tissues, especially 
in plants. It never makes a sound, it 
has no magnetic detecting devices, and 
it is transformed from one wavelength 
of light to another with extreme diffi- 

From this, one sees that while light 
energy is of such great importance to 

the human race, the things which it 
can be made to do are greatly limited. 
It can make us see, it can be recorded 
by a camera and it can be transformed 
into electrical energy by the photo- 
electric cell. 

The Photoelectric Cell 

How brief a recital this makes com- 
pared with the recital of electric en- 
ergy, which can be transformed quickly 
into other forms of energy, which by 
simple means controls almost any form 
of energy, and yet which itself is by 
nature so infrequently applied to the 
human system. It is very fortunate 
for us that one of our first light detect- 
ing instruments — the photoelectric cell 
— controls so universally applicable an 
energy as electricity. The human race 
has had for many years mechanical 
prime moves, mechanical legs and 
arms, and it has had electrical heaters, 
chemical heaters and so on, but the 
human race has been dependent upon 
the human eye for its detection and 
record of light. If the photoelectric 
cell can be made by a simple process 
to take the place of the human eye in 
certain places, it can be of great ser- 
vice to mankind. 

The Photoelectric Effect 

The photoelectric cell process is dis- 
tinct from the photo-chemical process 
in that light and electrons alone take 
part in it. If a zinc plate be sus- 
pended by a silk thread and charged 
with electricity from a static machine 
it will hold its charge for a long time. 
If, however, the light from an arc 
lamp be allowed to shine upon the zinc 
plate, it mil be found that, if the 
plate is charged negatively, it will lose 
its charge very rapidly under the ac- 
tion of the ultra-violet light from the 
arc lamp; but, if the plate is charged 
positively, it will retain its charge 
quite as well when the lig"ht is allowed 
to shine upon the plate as when the 
light does not shine upon it. This 
simple experiment will serve to illus- 
trate the effect known as the photo- 
electric effect. Since the plate loses 
the negative charge, but not the posi- 
tive, it is evident that the light causes 
the zinc to release electrons which are 
expelled from the zinc by its negative 
charge, just as heating the filament in 
a vacuum tube allows the filament to 
release electrons. 

Different metals than zinc will also 
release electrons when the light shines 
upon them. Experiments have shown 
that the light most powerful in its 
ability to release electrons from metals 
is the light of highest frequency, that 
is, violet or ultra-violet. The common 
metals such as iron, copper, gold, and 
platinum will release electrons only 
under the action of strong light in the 
extreme ultra-violet ; whereas experi- 

ment has also shown that certain of 
the metals, such as sodium and potas- 
sium, will release electrons under the 
action of visible light. The difference 
in the willingness of the various metals 
to release electrons is probably in part 
responsible for their chemical activity. 
It is quite evident that gold and plati- 
num are less active chemically than 
zinc, and in the same way zinc is less 
active chemically than are sodium and 
potassium. In fact, sodium and potas- 
sium are so active they cannot be kept 
in the atmosphere 'without quickly com- 
bining with the oxygen and the water 
vapor of the atmosphere and this com- 
bination renders their surface insensi- 
tive photo-electrically to visible light. 
It is for these reasons that photoelec- 
tric cells are made of sodium, potas- 
sium or similar metals and are made 
in the form of vacuum tubes, so that 
their surface may be preserved from 
chemical combination which will im- 
pair its photoelectric sensitiveness. 


(Continued from page 13) 
show they expected to get something 

I know when I'm tied, I couldn't 
argue with him. 

Well, the feature came and went, 
and the short stuff followed. When 
the trailers hit the screen, the non- 
sync blasted out with a popular fox 
trot with a vocal refrain. One that 
had been played over the radio for 

Explain the workings of that mind, 
if you can. 

We just gotta listen — and weep ! 


(Continued from page 28) 

parent inductance L a is then equal to 
R = W L„ where a> is 2*vf, or 377 at 60 
cycles. Where a standard reactor is 
used across the sample the calculations 

t, Ls T" Lx 

are: R = u, 

Lis A -iJx 

The third and last article of this 
series will comprise a resume of special 
amplifier circuits and the problems 
arising in the design of the completed 


T. E. Shea — Transmission Networks and 
Wave Filters. D. Van Nostrand Co. 

L. S. Palmer — Wireless Principles and 
Practice. Longmans. 

Glenn Koehler— Proc. IRE— Vol. 16. No. 12. 

S. D. La Voie — Unpublished notes. 

D. E. Replogle. Design of Iron Core Re- 
actances. Raytheon Tech. Bulletin Vol. 1. 
No. 1. 

The Use of Allegheny Electric Metal. 
Allegheny Steel Corp. Brackenridge, Pa. 

I-Ianna- AIEE Journal— Feb., 1927. 

Spooner— Phys. Rev. 192o page 527. AIEE 
Journal Jan., 1923. 

(To be continued) 

Page 36 

Projection Engineering, November, 1929 


A distinguished gathering of many of 
the foremost educators and business lead- 
ers of the country recently attended the 
first "all-talkie" dinner in history, at the 
Roosevelt Hotel. Every after-dinner 
speaker was presented through the 
medium of the talking film in the first 
official demonstration of a new advance- 
ment in visual and audible education. 

Sponsored by Talking Picture Epics, in 
association with the pioneer sound-picture 
organization of RCA Photophone, this 
dinner celebrated the entry into the educa- 
tional and industrial field of audible 
pictures. The recent statement of a lead- 
ing producer that the sound screen is 
the most perfect medium devised by the 
ingenuity of man to disseminate informa- 
tion, culture and helpful knowledge was 
demonstrated as a reality with the RCA 
Photophone talking film and portable 
sound projector in the role of public 
speaker, lecturer and guide. 

George Palmer Putnam, publisher, and 
himself a celebrated explorer, headed the 
list of "talkie" speakers as the celluloid 
toastmaster of this unique occasion, de- 
scribing the manifest advantages of mak- 
ing a public address without having to 
survey the dismayed faces of after-dinner 
speech victims. All the mannerisms, smil- 
ing gestures and motions of Mr. Putnam 
were faithfully projected on the screen 
together with a perfectly reproduced echo 
of his voice, as he genially spoke his 
witticisms on this new manner of public- 

The full purpose of the occasion, the 
placing in the hands of educational, wel- 
fare and business groups of this new tool 
of public approach, was described by E. 
E. Bucher, executive vice-president of 
RCA Photophone. He predicted that 

events of this kind would be commonplace 
within a few months, and declared that 
the world-wide interest of the people in 
talking pictures as entertainment would 
be similarly reflected in their acceptance 
of them as a new and enlivening method 
of education. 


Striking progress in Europe in the 
transmission of photographs by radio is 
reported by Major R. H. Ranger, Design 
Engineer of R.C.A. Communications, Inc., 
who just has returned from a tour of obser- 
vation there. Major Ranger, who perfected 
the facsimile device controlled by the 
Radio Corporation of America, said the 
evident spirit of cooperation on facsimile 
transmission in European countries was 
exemplified by Marconi's remark to him 
when he was leaving England for Ger- 
many, that he was at liberty to tell the 
Germans everything he had seen of his 
work and that he would appreciate any 
report on German work, with the permis- 
sion of the Germans. Dr. Schapira of 
Telefunken in Germany, immediately 
granted the permission. 


With exhibitors in convention through- 
out the country heralding the develop- 
ment of the RCA Photophone low-priced 
sound system as the most progressive 
step toward saving their small theatres, 
Sydney E. Abel, general sales manager, 
stated' that this equipment, known as the 
Type G, will definitely be on the delivery 
schedule for December. 

Factory production is proceeding at 
top speed to complete a huge first order 
for the December contracts. The rapid- 
ity with which theatre owners contracted 
for this $2905 combined sound-on-film and 

sound-on-disc system is taxing the manu- 
facturing divisions of RCA Photophone to 
capacity. More than 1500 men are work- 
ing on the Type G equipment at the 
Schenectady plant of the General Electric 
Company, and approximately 1200 are 
operating full schedules in the great East 
Pittsburgh plant of the Westinghouse 
Electric and Manufacturing Company. 
Both manufacturing associates of RCA 
Photophone will be required on steady 
factory schedule from now until Decem- 
ber to complete the first delivery of the 
Type G reproducing system. 

Mr. Abel makes positive assurance that 
this theatre system will be delivered for 
the first contracting theatres by the initial 
week of December. The first of the year, 
he declares, will find more than 150 
systems installed with subsequent installa- 
tions proceeding at an almost equal rate. 


A very interesting installation of sound 
equipment manufactured by the Amplion 
Corporation of America, has been com- 
pleted recently at the Mayfair Theatre in 
Newark, New Jersey. This is a motion- 
picture house, seating 1200 persons. 

Two new-type Amplion turntables are 
utilized — one for each projector. Each 
turntable is driven by its respective pro- 
jector motor, through a chain drive. 

The amplifier is a double channel, type 
2P2A Amplion product. Each channel con- 
sists of a separate three-stage amplifier, 
employing two -26-type tubes, one -27-type 
tube, two -50-type tubes in push-pull and 
two 281 half-wave rectifiers. Van Home 
tubes are used throughout. 

The double channel amplifier is arranged 
so that either channel can be put into 
operation by merely throwing a switch. 
Hence, if any small trouble should de- 
velop in one of the channels, the other 
one is always ready as emergency equip- 

Each amplifier is provided with one of 
the new Amplion constant impedance 
faders. These regulate the volume of the 
sound without altering the frequency 
characteristic of the phonograph pickup or 
the input transformer to which it is con- 

With the exception of the loudspeakers, 
all equipment is installed in the operator's 
room. A small monitor speaker, hung on 
the wall of this room, enables the opera- 
tor to check up on the operation of the 
complete equipment. 

Two ten-foot exponential air column 
horns are used, in conjunction with two 
type AA-102 Amplion Giant dynamic 
units. These are placed directly behind 
the screen on the stage. They are tilted 
slightly downwards, since the acoustics 
of the theatre require this. This is an 
example of an important advantage of the 
horn type speaker over the cone type. 
The latter is non-directional and in gen- 
eral is unsuited for talking-picture work. 

Both speakers are used at once, al- 
though either one may be used separately 
in an emergency. Even one speaker will 
furnish more than sufficient volume to 
reach the back of the theatre. The speak- 
ers are connected to the amplifier by wir- 
ing run in conduit. 


Faithful reproduction and maximum 
volume can only be obtained when there 
exists a perfect balance between all com- 
ponents of a sound-amplifying and re- 
producing system, according to Clifford 
E. Stevens, Chief Engineer of the Stev- 
ens Manufacturing Corporation of New- 
ark, N. J. 

"Several vears of intensive effort to at- 
tain the superlative in tone quality," 

states Mr. Stevens, "has taught the in- 
dustry the importance of properly 
matched audio units, including the match- 
ing of the impedances of amplifier out- 
put and loudspeaker input. However, 
there is still a weak link in the usual 
sound reproducing system, and that is the 
balance between the voice coil and the 
diaphragm of the dynamic loudspeaker. 
In many instances, the designer of the 
loudspeaker goes from one type of dia- 
phragm to another, using the same voice 
coil, and hastens to report that the orig- 
inal diaphraghm is more satisfactory. Ob- 
viously, the original diaphragm may be 
better matched to the voice coil than the 
second diaphragm. In other words, the 
voice coil should be matched to the dia- 
phragm, with the electrical impedance 
matching the mechanical impedance. 
There is a vast difference between most 
of the paper diaphragms and the newer 
burtex or fabric diaphragms, hence the 
loudspeaker designer should make due 
allowance in the voice coils employed." 


Among the many recent shipments of 
RCA Photophone recording and reproduc- 
ing equipment for studios and theatres 
in the British Isles and on the Continent 
are two improved-type RCA Photophone 
sound location trucks for the Gaumont 
producing studios in England, the foreign 
department of Photophone announces. 
These trucks embody the newest design 
in technical facilities for remote sound 
recording on film. 

These new sound camions contain 
special microphone amplifiers and mixing 
units which permit the sound technician 
to operate his sensitive microphones hun- 
dreds of feet from the truck. He can 
operate directly at the camera, keeping in 
communication with his recordist in the 
truck by means of a telephone wire line. 
The great advantage of these new RCA 
Photophone sound trucks over any other mo- 
bile recording units lies in this feature, 
which allows the microphones to be car- 
ried 10 floors into a building, up a moun- 
tain, out into a body of water, or into any 
hitherto inaccessible point of operation 
remote from the truck and its equip- 


Through the introduction of the one- 
piece fabric diaphragm for the usual 
dynamic speaker, appreciable savings are 
being scored in the radio industry, as re- 
flected in the new low price levels. Here- 
tofore, with the usual paper for the 
diaphragm, it has been necessary to cut 
the paper to size and shape, then form it 
into a cone, followed by mounting the 
cone with a flexible rim of soft leather 
and an outer support ring of heavy 
cardboard, for the , proper mask. This 
work has had to be "done by skilled girls, 
and has represented a slow and costly pro- 
cess. In brief, cone mounting has been 
the bottleneck of dynamic speaker pro- 

Many of the dynamic speakers this 
year, in marked contrast, are employing 
the fabric or burtex diaphragm, which 
comprises a special impregnated cloth 
pressed to the desired shape and then 
treated with a metallic lacquer. Such a 
diaphragm can be made in practically any 
shape and size, with curved as well as 
straight sides, and also with any rim, 
bead, voice coil mounting, flexibility, and 
so on, as contrasted with the elaborate 
assembly yet inflexibility of the usual 
paper cone. The present practice is to 
make the fabric cone in one piece, with 
diaphragm, supporting rim, mask and 
voice coil mounting, complete. Thus the 

Projection Engineering, November, 1929 

Page 37 

A cure for Line Voltage Ills! 

NO longer is it necessary for your 
talking picture equipment to be 
at the mercy of fluctuating line volt- 
age. You can be absolutely indepen- 
dent of all fluctuations by including 




The giant variable re- 
sistor, which, in several 
turns of the knob, pro- 
vides a wide resistance 
range. Handles 250 
watts. Available in 
14-10, 25-500, and 
200-100,000 ohm 







Provided with extra 
long nipple for mount- 
ing on slate or marble 
panel, and with special 
bracket for mounting 
on bakelite panel. Also 
ideal as variable speed 
motor control and gen- 
erator field control. 


117 D I TH C* regarding this and other CLAROSTAT devices which, 
* * *^ * * *-* having set a high mark in radio, are now available for the 
peculiar requirements of picture projection and sound reproduction. 


Specialists in Radio Aids 
296 N. 6th St. -:- Brooklyn, N. Y. 

Page 38 

Projection Engineering, November, 1929 

loudspeaker manufacturer eliminates 
costly assembly of diaphragms, which is 
the bottleneck of his production. In the 
case of one well-known radio set manu- 
facturer, making upwards of 5,000 high- 
grade sets a day, a saving of 20 cents 
per dynamic speaker has been effected 
by means of the one-piece burtex cone, 
representing a saving of at least $1,000 
per day, not to mention the speeding up 
of loudspeaker production in that plant. 


Following a meeting of the Board of the 
DeForest Radio Company, James W. Gar- 
side, President, announced that the No 
Par Capital Stock of the company had 
been increased 345,680 shares through the 
exchange of DeForest Common Stock for 
that of Jenkins Television. The exchange 
was on the basis of one No Par Common 
share of DeForest Radio for each 1% 
No Par Common shares of Jenkins Tele- 
vision. The offer of exchange expired 
Friday, Oct. 18, 1929. 

With 984,652 shares of DeForest pre- 
viously outstanding and the additional 
345,680 shares through the exchange, the 
total stock of DeForest Radio authorized 
to be outstanding is now 1,330,332 shares. 
Application for listing the additional 
shares has been made to the New York 
Curb and the Los Angeles Stock Ex- 

Mr. Garside also announced the election 
of Kelly Graham, President of the First 
National Bank of Jersey City, to the 
Board of the DeForest Company. 


The demand for General Amplifiers has 
been increasing so rapidly that the com- 
pany has recently appointed the follow- 
ing ' representatives : 

Mr. "Walter W. Boes, 622 Broadway. 
Cincinnati. Ohio, who will cover the terri- 
tory of Southern Ohio and Northern Ken- 
tucky ; and Mr. G. J. Spencer, 29 Steward 
Street, Detroit, Michigan, who will handle 
the General Amplifier line in and around 
Detroit. Mr. V. A. Hendrickson, c/o 

Martin-Copeland Company, 87 Maiden 
Lane, New York City, will cover the 
territory of Metropolitan New York, Phila- 
delphia, New Jersey and Southern Con- 


The field of news movies has undergone 
a tremendous transformation during the 
past year, according to J. E. Smith, 
President of the National Radio Institute 
of Washington. "Whereas a man could 
become a news cinematographer for an 
investment of a few hundred dollars for 
his outfit, together with a few months of 
experience, it is now necessary to have a 
sound recording outfit and the accom- 
panying experience as well. The news 
cameraman must now be versed in micro- 
phone, amplifying and recording work. 
In fact, most of the news reels are rapidly 
going to complete sound presentation, so 
that the news cameraman must necessarily 
know his radio quite as well as his photo- 


Edward Auger, prominent in the film im- 
porting and exporting field, has been 
named General Assistant Sales Manager of 
RCA Photophone, Inc., it is announced 
by Sydney E. Abel, General Sales Mana- 
ger, concurrent with heavy exhibitor de- 
mands for RCA Photophone's new low- 
priced sound equipment. 

Mr. Auger comes to RCA Photophone 
after 23 years in the motion picture in- 
dustry. He was general sales manager of 
the Vitagraph company for a number of 
years, and later transferred his activities 
to the exporting and importing of pic- 
tures. Mr. Auger was the managing di- 
rector of the Fox interests in Paris, and 
represented French Pathe in its raw stock 
sales in this country. 

With nearly a quarter of a century of 
sales direction in the motion picture field, 
Mr. Auger's experience internationally and 
with the American exhibitor will be of 
great value in caring for the tremendous 
volume of business in RCA Photophone's 
Type G reproducing system. 


A. J. Carter, "daddy" of the Radio 
Manufacturers' Association, >pioneer in 
television, and president of the Carter 
Radio Company of Chicago, startled the 
radio and motion picture worlds recently 
with two predictions. 

"Television for commercial use, available 
for millions of homes, will be an actuality 
within the present year," was one predic- 

"Talkies, and music from films, will be 
common in the home also within the 
year, was the other. 

Mr. Carter's company was the first in 
the world to demonstrate publicly the 
sending of pictures with sound, over 
broadcasting wavebands. That was at the 
Stevens Hotel in Chicago a year ago last 
June. Later he successfully demonstrated 
at the New York and Chicago Radio 
shows. And he also was first in the 
world to successfully send pictures to a 
moving airplane. 

And now his company has abandoned 
air television entirely as a practicable 
commercial proposition. The immediate 
future of television lies in the use of the 
country's vast system of power lines. 


Pres., Carter Radio Co. 

Within the year, Mr. Carter said, all you 
will have to do is to plug into a light 
socket, and enjoy perfect pictures of the 
broadcasting station from which you are 
receiving your radio programs. 

"Nothing new in it," the big radio 
parts man said. "Television over wires 
was thought of more than 40 years ago. 
We've merely developed the theory and 
idea practicably. The use of television 
will be low in cost, in fact the device will 
cost less than a radio, and so simple to 
operate that there will be nothing to it 
but plugging into a light socket, and 
turning a knob." 

Air television, Mr. Carter said, has 
been proved impracticable for commer- 
cial use. The "spotting" of the picture by 
the least disturbance, plus the national 
commission's holding to the theory that 
television should be practised on short 
wavelengths, plus the fact that monopoly 
of the air by advertising and programs 
give television too few air channels — all 
these bar the aid, he said. But by super- 
imposing one frequency upon the other, 
the power line can be used to transfer 
the picture in perfect detail — and without 
interfering in any way with the normal 
functioning of the power line. 

"It means that every room with a light 
socket can have television," he said. "Set 
the little box on top of the radio, or any- 
where else you please, and see the picture 
without flaw. Your television device will 
not be a part of your radio set. It will 

be wholly independent and suffer none of 
the difficulties of air transmission. 

The home talkie prediction by Mr. Car- 
ter was born of the successful experiments 
his experts have conducted from almost 
the beginning of the industry. By adapt- 
ing the light frequency, sound track 
system employed in the talkies, a home 
device will furnish music by film for 
hours without requiring changing or 
manipulation, and from the same device 
talking pictures can be had when wanted. 
This device, too, will be low in cost to 
the public, and simple of operation. 


Of considerable interest to the trade is 
the fact that The Daven Company is in 
full production of the same products as 
manufactured by the former organization, 
The Daven Corporation, the Resistor Spec- 
ialists. Mr. Lewis Newman, of Newark, 
N. J., is the President. 

Continuing the policy of the former com- 
pany this new organization has been able 
to show a marked increase in volume of 
business, and numbers among its custom- 
ers many of the prominent manufactur- 
ers of electrical, radio, moving picture 
projection, and television apparatus. 

Modern equipment has been installed in 
the tube division of the plant and the 
company is in full production of all types 
of tubes. 


A finance plan designed to aid motion 
picture theatre owners in this country in 
the installation of talking pictures equip- 
ment in their theatres has been completed 
between BCA Photophone, Inc., manufac- 
turers of sound-picture equipment, and the 
Commercial Investment Trust. Inc. Under 
this arrangement, the C. I. T. will finance 
the transactions involved in the leasing of 
the sound-picture equipment manufactured 
by RCA Photophone for exhibitors. This 
equipment is leased to the theatre owner 
on a ten-year basis, rental for which is ex- 
tended over a period of three years, pay- 
able monthly. 


With the beginning of the Fall school 
term, the radio loudspeaker has taken its 
place beside the blackboard as an aid to 
teaching. According to Quinton Adams, 
vice-president of the Radio-Victor Cor- 
poration of America, twenty schools in 
various parts of the country have begun 
the new term equipped with centralized' 
radio apparatus for the distribution of 
educational programs to the classrooms and 
between sixty and seventy other schools 
are planning similar installations. Every 
school year brings an extension of edu- 
cation by radio. 


A basic patent on the method of making 
loudspeaker diaphragms of fabric, has just 
been granted to the Stevens Manufacturing 
Corporation, according to the statement of 
Clifford E. Stevens, Treasurer and Chief 
Engineer of the organization. 

"Patent No. 1,729,407, just issued to us," 
states Mr. Stevens, is exceptionally broad 
and therefore may be considered basic. 
We have been allowed seventeen claims on 
the method of making loudspeaker dia- 
phragms of fabric. Our patent covers the 
method of making large, direct-acting, 
acoustic diaphragms of conical form, by 
stretching a continuous piece of flat-woven 
fabric impregnated with stiffening material 
in a moist condition over a form to shape 
the fabric, without lapping, and to tension 
it in all directions until the stiffening 
material has become set ; and thereafter 
applying to the diaphragm a material to 
fill the interstices in the fabric and to 
waterproof and further stiffen the fabric. 
That is essentially the process employed in 
making the well-known Burtex diaphragms. 


The Radio-Victor Corporation of America 
has begun preliminary production of the 
first commercial models of the Theremin 
"ether wave" musical instrument, which is 
played by simply moving the hands in the 
air above it, according to an announcement 
by E. A. Nicholas, vice-president in charge 
of the Radiola Division of Radio-Victor. 
Mr. Nicholas disclosed that the RCA has 
acquired an option on the exclusive patent 
rights from Professor Leon Theremin, the 
young Russian scientist who invented the 

Projection Engineering, November, 1929 

Page 39 




ROLA loudspeakers, Ions: noted for their 

quality, are now provided for every purpose 

demanding the utmost in fine sound repro- 

These electro-dynamic loudspeakers operate at 
approximately twice the sensitivity of competing: 
dynamics, yet without increase of field energizing 

Kola reproducers have proven rugged and depend- 
able under the most exacting conditions. The 
Kola exclusive welded-to-housing construction, 
adjustable center pole tip, ventilated field wind- 
ings, and moisture-proof materials insure repro- 
duction of unusual reliability. 

The highly desirable compactness and simplicity 
of the Rola loudspeakers is apparent at a glance. 
A side-by-side comparison will quickly demon- 
strate their superior reproduction qualities, Kola 
provides the consistently brilliant and reliable 
performance required today by your users. 

The Kola model illustrated above is C-90; an electro-dynamic 
unit with 9-inch diaphragm, field coil wound to 2500 ohms, 
75 to 150 volts D.C. It is especially well adapted to amplifiers 
using 245 tubes in push-pull combination — for radio receiving 
sets, electric phonographs, and auditorium installations. 

Inquiries for details, blueprints and prices 
from responsible manufacturers are solicited. 


2570 E. Superior Ave. 

45th & Hollis Sts. 


IwistecrDiting leeth 
°f Steel 

TIGHTEN the nut against the SHAKEPROOF 
Washer and it's there to stay. Gripped by 
twisted steel teeth, around the whole circum- 
ference, it can't loosen — applied pressure with 
a wrench alone can break its hold. SHAKE- 
PROOF Lock Washers were developed for one 
purpose — to lock nuts. That they do this 
superlatively well is indicated by their univer- 
sal adoption in over a hundred and fifty differ- 
ent American industries. Today SHAKEPROOF 
is the standard lock washer. It should be on 
your product. Let us send you samples to 
prove to yourself the merits of SHAKEPROOF. 

Lock Washer Company 

^ [ Div.sion of Illinois Tool Works ] "* *- 

3509 North Keeler Avenue Chicago, Illinois 

U.S. Patents 1,419,564; 1,604,122; 1,697,954. 
Other Patents Pending. Foreign Patents. 



2509 North Keeler Ave., Chicago, III. 

Please send me samples of 

D Shakeproof Lock Washers to fit bolt sire 

O Shakeproof Locking Terminals, size 

Firm Name 


Town State 

By. .. , ■ , „____ 

Page 40 

Projection Engineering, November, 1929 


The Binks Manufacturing Company, 3114 
Carroll Avenue, Chicago, announces the 
completion of an all purpose utility spray 
painting and finishing outfit, known as the 
Binks New Hurley Unit. 

This outfit is being manufactured on a 
large production basis for general utility 
work such as touching up, refinishing, re- 
painting, and lacquering practically any 
product within an organization. 

It is a complete unit equipped with a 
full size quart all metal container and a 
New Binks Pressure Cup Spray Gun supply- 
ing an atomized flat spray four inches in 

The air compressor unit is belt-driven 
and connected to a % H.P. General Electric 
motor. This unit has a capacity of 2.16 
cubic feet of air per minute. 

The outfit is sturdily constructed. A rib 
cast iron air container is mounted between 
the motor and the compressor on a pressed 

New Binks Spraying Unit. 

metal base all of which is mounted on rub- 
ber feet. The cylinder and base are cast 
in block of seasoned grey iron and accu- 
rately machined. 

Ten feet of rubber covered electric cord, 
attachment plug, and ten feet of durable 
braided rubber air hose are attached to the 

The Binks New Hurley Unit is complete 
ready for use upon delivery. 


To fill the demand for microphone mix- 
ing panels, the Electro-Acoustic Products 
Company, 55 E. Wacker Drive, Chicago, has 
developed a very efficient unit which is 
being standardized, and is now on the 
market. The microphone input panel 
illustrated in the photograph is particu- 
larly designed for recording studios, but 
can also be used for public-address work 
or wherever more than one microphone is 
employed in an amplifying circuit. 

The microphone panel CM-4 incorporates 
four individual faders or mixers for four 
condenser microphones so that any num- 
ber up to four microphones may be con- 
trolled separately or mixed together at 
will. Included also is a very novel feat- 
ure which has proven invaluable in the 
case of recording studios. This is a 
volume indicator meter which is operated 

from the main amplifier volume indicator 
tube. By means of this meter which has 
a 5-inch scale, the operator can accu- 
rately control the input, and at the same 
time watch his talent in the studio, also 
making it possible to install the control 
apparatus remotely from the amplifying 

Rear view of the microphone input 
panel, showing the shielding. 

The unit is thoroughly shielded, the 
parts being mounted on a steel panel and 
covered by a steel can. This is absolutely 
essential where high amplification is 
used, and noiseless results are expected. 
Mixing controls mounted on bakelite 
panels frequently pick up alternating-cur- 
rent noise, and generator brush noises. 

The mixing panel CM-4 is designed for 
200-ohm input and 200-ohm output. The 
output impedance of the unit is always 
constant at 200 ohms regardless where 
the controls are set. 


What might well be termed a super- 
dynamic speaker, has just appeared on the 
market under the Powerizer trade mark. 
This new speaker, manufactured by the 
Radio Receptor Company of New York City, 
has a frequency range of from 40 to 8,000 
cycles, with an effective frequency response 
of from 40 to 6,000 cycles, it is said. In 
addition to this unusual frequency range, 
the new speaker is guaranteed to handle 
10 watts undistorted output in constant 
use, which guarantee is considered con- 
servative, since the speaker has been oper- 
ated with as high as 30 watts undistorted 
output, without signs of distress. 


A new power supply has just been de- 
veloped that eliminates the last battery 
necessary in talking motion-picture theatre 
sound installations. Hitherto, all sound-on- 
film apparatus required a storage battery 
for the exciter-lamp as well as the head- 
amplifier tubes. This new power supply, 
designed and manufactured by the Radio 
Receptor Company of New York City, sup- 
plies the necessary current to the exciter- 
lamp and the head-amplifier tubes, as well 
as the B supply for the latter. There is 
absolutely no increase in hum level, above 
that present in the battery-operated ap- 

The special Powerizer voltage compen- 
sator is included in this new power sup- 

ply, and it is stated, regulates the line 
voltage so closely that between 100 and 
130 volts variation on the line, there is 
a corresponding variation of not more than 
13/100 of 1 per cent. This astonishing ac- 
curacy is due to the special design of this 
compensator, which is of the transformer 
leakage type. 


The Hainmarlund Manufacturing Com- 
pany, of 438 West 33rd St., New York 
City, have introduced a new series of audio- 
frequency transformers for use in power 
amplifiers, and power transformers designed 
for use with power units employing full- 
wave rectifiers. 

The first stage audio-frequency trans- 
former, AP-2, has a ratio of 1% to 1, 
while the ratio of the push-pull input trans- 
former, AF-4, is 2 to 1, on each side. 

The primaries of both transformers are 
very large. This coupled with the use of 
treated laminations grouped in a special 
way into unusually large cores permits uni- 
form amplification from as low as 46 cycles 
to as high as 4,800 cycles. 

One of the output transformers, AF-M, 
is an impedance matching unit designed to 
match -45 tubes to magnetic speakers, 
while the other AP-D, works directly into 
the moving coil of a dynamic speaker. This 
unit takes the place of the impedance 
matching transformer usually supplied with 
the speaker. The large cores of treated 

New Hammarlund a-f transformer. 

Front view of Electro-Acoustic microphone input panel. 

laminations which are also used here, pre- 
vent current saturation, thus affording true 
energy transfer. 

All these transformers are enclosed in 
enamelled steel cases with pigtail terminal 
leads for sub-base connection. 

The power supply unit, PS-45, consists 
of a pair of 30-henry chokes and of a high 
voltage transformer, with a 110-volt pri- 
mary, tapped at 80 volts for use with a 
voltage regulator. The high voltage sec- 
ondary has an output of 750, is rated at 
100 mils, and is center tapped. There 
is also a 5-volt, 2-ampere center tapped 
winding for supplying filament voltage to 
an -80 tube; a 2y 2 -volt, 3-ampere center 
tapped winding for the filaments of a pair 
of -45 tubes, and a 2% -volt, 9-ampere 
winding for the heaters of five -24 or -27 

Projection Engineering, November, 1929 

Page 41 



A public address system is no better than its 
microphone. Unless the microphone is right, 
the best of transformers, filters, tubes and 
speakers are of no avail. Unlike the average 
public address microphone which is sensitive only 
to a few frequencies in the voice range, the 
microphone regularly furnished with Ampli- 
sound responds to all frequencies between 30 
and 10,000 cycles, every point in the vocal and 
musical range — and even beyond. Every com- 
ponent part in Amplisound is selected with equal 
care, subjected to searching tests, adopted only 
when perfect. 


ample sound 

Amplisound Systems reproduce voice, music, 
radio programs, talking picture discs, records — 
and they are attractively priced. Amplisound 
engineers will gladly work with you on any 
problems relating to sound reproduction. Write 
for full information. 

Amplisound Systems 


224 North Desplaines Street 


as well as the picture 

THE Weston Model 547 is a complete testing 
outfit — lightweight, portable and simple to 
operate — which is universally popular in radio 
servicing work, and ideally designed for the periodic 
inspection and maintenance of sound projection 

Model 547 provides for all the required tests of 
amplifiers, tubes and circuits — insures the delivery 
of proper plate voltage, guards against distortion and 
enables the service engineer or operator to quickly 
locate troubles and make necessary adjustments so 
that correct performance of the equipment and 
operating protection will be assured. 

Equipment companies, theatres, and all those who 
have a financial or operating interest in moving 
pictures and sound reproduction should investigate. 
Send for descriptive information. 

608 Frelinghuysen Ave., Newark, N. J. 

Page 42 

Projection Engineering^ November, 1929 





The Pacent Electric Co. announce three 
new models of the Pacent Phonovox elec- 
tric pickup, specially designed to give 
maximum efficiency with new model, all- 
electric, screen-grid receivers. The new 
series 106 Super Phonovox models embrace 
a number of improvements to secure the 
utmost quality and volume from electrically 
recorded records when played through the 
modern power amplifier or radio receiver. 

The new type changeover switch gives 
an instant change from radio to record 
entertainment by merely turning a single 
knob. No electric connection changes are 
required when going from one to the other. 
Formerly, it was necessary to change cer- 

The Pacent Phonotrol Adapter. 

tain connections. The Phonotrol adaptor, 
used with the new changeover switch, fits 
easily over the prongs of the 5-prong type 
detector tube. It was designed to meet 
the demand for a device which would give 
better results and greater volume with 
new type receivers using 5-prong, a-c. de- 
tector, and screen-grid tubes. 

The new 106 Phonovox are announced as 
having a greatly increased frequency cover- 
age, from 50 to 8,000 cycles, which more 
than covers the range of commercial phono- 
graph records. Special English 36 per 
cent cobalt magnets, accurately counter- 
balanced tone arm giving exact needle 
pressure and minimum wear of records, 
elimination of all rubber bearings and fold- 
back hinge for easy needle changing are 
among the features of the new Pacent 

The new type electric phonograph motor 
is specially designed with the requirements 
of radio-phonograph combinations in mind, 
where elimination of sparking and all vi- 
bration, is of paramount importance. The 
Pacent motor is of the squirrel cage in- 
duction type, and is completely insulated 
against noise. There are no commutators 
or brushes, and consequently no radio inter- 
ference. It has unusually high starting 
and running torque. 

Pacent Super Phonovox Pickup. 

The new motor operates equally well on 
either 50 or 60 cycles, 110 v., a-c. 

Pacent has also introduced a complete 
new line of power amplifiers in assembled 
form. They are unusually compact units, 
housed in sturdy metal cases. Tube 
sockets are left in readily accessible posi- 
tion outside the housing, while all other 
parts are encased to keep out dust and 
prevent possibility of shock at high volt- 
age points. 

In addition to the new Phonovox pick- 
ups, the electric motor, and the amplifier 
line, Pacent has introduced a new line of 
small size transformers, including power, 
output and push-pull types. The Electro- 
vox, a complete pickup and turntable unit 
for reproducing records through the radio 
set, gives the owner of a good radio re- 
ceiver, results obtainable only with the 
high priced phonoradio combinations. 


The requirements of the educational in- 
stitution differ radically from those of 
other public places when it comes to sound- 
reproducing installations, according to Lud- 
wig Arnson, Vice-President of the Radio 
Receptor Company of New York. Whereas 
the restaurant, dance hall, stadium and 
other applications continually reproduce 
the same type of program and generally 
from the same source, the school repro- 
duces a variety of subjects from manv 
different parts of the building. For this 
reason, the school or educational installa- 
tion must be far more flexible than the 
usual installation, if it is to prove of 
maximum worth. 

The Radio Receptor Company has just 
perfected an all-purpose amplifier panel, 
especially designed for school and similar 
educational applications. The panel board 
includes a radio set, a three-position micro- 
phone and mixer, a switch panel, a volume 
control panel, a microphone amplifier, and 
two power amplifier panels. This installa- 
tion makes it possible for the principal of 
the school to address the entire school. 
Visiting speakers may likewise be heard 
throughout the building as well as in the 
auditorium. Educational and similar fea- 
tures may be picked up by radio. Recorded 
music is available by means of a phono- 
graph pickup. The switching panel makes 
it possible to employ all three mediums 
simultaneously, changing from one to the 
other by means of a single three-position 


The Radio Receptor Company of 106 
Seventh Avenue. New York City, announces 
a new line of microphones for public-ad- 
dress and sound reproduction purposes. 
These microphones have been designed pri- 
marily for use in conjunction with Power- 
izer sound amplifying systems. The pos- 
sibilities of their universal use have been 
fully appreciated, however, and they have, 
therefore, been placed on the market. 

There are three types of microphones in 
this new line, namely, a 3% -inch, a 6-inch 
and a hand microphone for portable use. 
The hand microphone is enclosed in a 
bronze case with bakelite handle. These 
microphones have been developed especially 
for public-address purposes, and incorpo- 
rate a number of features that make them 
particularly desirable in this field. The 
construction includes a special alloy dia- 
phragm that has no fundamental period of 
its own. There is also a special composi- 
tion carbon button that positively cannot 
"pack." This feature is particularly de- 
sirable in public-address apparatus where 
the microphones are generally located far 
from the home "Lab," and must conse- 
quently perform satisfactorily over long 
periods of time without attention. 


A brand new dynamic reproducer, known 
as the Racon Type "A" Giant Dynamic, 
has been developed especially for 'talking 
motion picture work. 

It possesses a frequency response covering 
the entire band of audibility from 60 to 
5000 cycles, it is said. 

A single horn equipped with the new 
type "A" unit and placed behind the screen, 
furnishes more than ample volume for a 
1500 seat house. 

The Racon reproducer combines the un- 
questioned advantages of horn-type speak- 
ers with the good features of cone-type 
dynamics. It has none of the surface 
noises characteristic of the paper dia- 
phragm dynamics. The resonance of the 
paper diaphragm is absent in the Racon, 
since the latter uses a very light metallic 
diaphragm. The resonant point of the 
Racon diaphragm is above 10,000 cycles and 
hence cannot interfere with reproduction. 

The light metal diaphragm utilizes a 
new patented method of cloth suspension. 
The diaphragm is dome-shaped and has 
great strength. The cloth used for sus- 
pension is chemically treated and is fast- 
ened at several points. Due to this new 
type of suspension, the diaphragm is cap- 
able of relatively great movement, without 
the slightest chance of cracking. 

The Racon Giant is designed to operate 
on an output up to 30 watts of undistorted 
power. It requires a field supply of 1 
ampere at 6 volts direct current. The 
unit can be used in connection with any 
well-designed horn, although best results are 
obtained by using the special process 
Racon air-column exponential horns, espe- 

cially constructed for theatre and public- 
address work. Although the Racon type 
"A" Giant Dynamic has been developed 
primarily for talking motion pictures, it 
can be used to great advantage for all pub- 
lic-address work. It is unaffected by 
changes in temperature or humidity and is 
weatherproof in construction. 


The Miles Manufacturing Co., 31 West 
21st St., New York City, have introduced 
two special horns for talking picture and 
public-address use. 

The Miles "Trumpet" Horn for public- 
address work is of the exponential type, 
with a morning glory flare, and is 3% feet 
long. The material of which the horn is 
made is water-, weathsr- and moisture- 

The new Miles 
"Trumpet'' Horn. 
Below: The Miles 
M 10 exponential 

The Miles "Trumpet" Horn lists for $170, 
which price includes an electrodynamic air 
column speaker unit and a 4000-ohm out- 
put transformer. 

The Miles M 10 Horn, used principally 
for talking pictures, but well adapted for 
other uses, has a ten-foot exponential air 
column, is 36" deep and has a bell 42" 

square. The horn cuts off at 50 cycles and 
its frequency range extends above 5000 
cycles. This horn is made of the same ma- 
terial that goes into the Miles "Trumpet," 
The list price is $125, or with a Miles 
electrodynamic speaker unit and a 4000-ohm 
output transformer, $275. 


The GoldE Manufacturing Co., 2013 Le 
Moyne St., Chicago, have introduced a new 
Lens Mount having a number of excellent 

It is claimed that the GoldE Lens Mount 
permits a change of lenses in three seconds 
and while the machine is in operation — and 
at the same time affords the same size 
screened picture for both Movietone and 
Vitaphone. Furthermore, this new lens 
mount has no up and down adjustments 
and cannot be shaken out of focus or po- 

Projection Engineering, November, 1929 

Page 43 

The Burt Reproducer for Talking Motion Pictures 

Burt Reproducer on Powers Projector 


Synchronous Motor Drive (110 or 220 volts, 50 
or 60 cycles). Prevents variation in speed 
from variation in line voltage, or projection 

The Super Cells used require only two stages in 
head amplifier, hence less distortion. 

Ease of Threading. When running disk or silent, 
the Sound-on-Film unit is not threaded. Sound- 
on-Film threads as easily as through a Powers 

Turn Table Is Accessible, being up high at the 
side of the machine. 

Easy to Install. Installation can be made by 
the ordinary operator, and wire man. 

Projector Head is driven by its main drive gear 
and is not required to drive any part of the 
sound equipment. 

Only Three Shafts: (1) Motor Drive Shaft, 
(2) Sound Film Shaft, (3) Disk Table Shaft. 

Variable Speed can be used for making schedule 
by driving the head off the Powers Motor, when 
running silent. Change from synchronous drive 
to variable speed drive requires about ten 

No Universals — No flexible couplings, flexible 
shafts, or long unsupported shafts are used, as 
these produce tremolo. 

Fire Hazard Is Decreased by use of this equip- 
ment. Failure of take-up does not cause film 
to pile up in light. 

Write for Bulletin No. 291 

Developed by R. C. BURT Scientific Laboratories, 
Pasadena, California 

Manufactured by 


9035 Venice Boulevard 
Los Angeles California 





FOR YEARS the name of CROWE has 
been synonymous with fine escutcheons 
and name plates, and the demand for 
CROWE products in the radio, phono- 
graph, and electrical fields attests to this 

WE ARE prepared to submit to manu- 
facturers in the sound and light projec- 
tion industry samples and estimates on 
name plates, segments, dials, scales, spe- 
cial embossings and escutcheons. 

CROWE ENGINEERS will give careful 
personal attention to each manufacturer's 
problems, and invite consultation — with 
rio obligation on your part. 

"Travel by Air - - - Use Air Mail" 

Crowe Name Plate 8 Manufacturing Company 

175 6 Grace St., Chicago, 111. 




made by the largest manufacturers 
of radio set essentials in the world, 
and the choice of 80% of the great radio 


ready to lend their 

jrers, , 
famous Quality 


Dependability to 
the great new industry of Sound Projection. 

For Amplifiers: — Polymet high-wattage resistors 
Poly met high-voltage filter condensers. 

For Equalizer Networks: — Polymet small fixed con- 
densers — Polymet resistors. 

For Power Transformers, Audio Frequency Trans- 
formers, Impedance- Adjusting Transformers, Loud- 
speaker Units: — Polymet Coils ("Polycoils") 

jfik Send for our catalogue giving complete specifi- 

^^^ iB cations of Polymet Products. 

4^HHbuQR We will gladly supply samples and work with 

m| yjHlBE you to meet particular specifications. 

•nflp Polymet Mfg. Corp. 

■ 839-A East 1 34th St. 

^ New York City 

IPolymet Products 

Page 44 

Projection Engineering, November, 1929 











Write for Catalogue Describing Microphone Stands, Cords, and Spring 

THIS system is UNIQUE. It incorporates a mixing pamel 
which allows the use of two microphones, a phonograph 
pickup, and a screen-grid radio receiver either singly or at 
the same time. This unit may be modified to suit any require- 
ments. The complete system, is capable of supplying power 
to upwards of 200 speakers, making it suitable for every form 
of program distribution service, and in addition to the mixer 
includes a voltage amplifier and power level indicator panel, a 
power amplifier panel, and rectifier, filter and power panels. 

The outstanding electrical features are: The entire system is 
operated from the A C line and may be operated at full gain 
without an appreciable hum. 

One power supply for A, B, and C voltages, resulting in econ- 
omy in cost and operation since there is no duplication of parts 
as in systems where separate power supplies are used. 

It incorporates the latest development in rectifiers, the Hot 
Cathode Mercury Vapor type. The low tube drop of this type 
together with the low resistance filter system, results in a 
power supply with excellent regulation, allowing the use of the 
multiplicity of stages on a single power supply. 

Meters are provided for reading microphone button current and 
space current in the output amplifier tubes. Simply press a 
button and the desired current is read on the meter. 

The comparatively high power output available allows its use 
in ordinary installations at far below the overloading point 
with all the obvious desirable features thereof. 

The entire system is mounted on a standard A-type rack on 
metal panels with crackle enamel finish, dust covers being pro- 
vided for each unit. 


222 Grove Street 

PHOTO CELLS, neon lamps, special high 
vacuum or gas filled tubes, and noise-free 
liquid grid leaks, manufactured to specifications. 

150 West 22nd St. New York City 

Chicago: Fred Carrier Co., 9 S. Clinton St. 
San Francisco: C. C. Langevin Co., 274 Brannon St 


All Kinds from $10 to $300 

For Public Address, etc., list $25 

Standard Broadcast Model, list $75 

Condenser Models for Film and Record Work, 

list $250.00, $300.00 

Also Desk and Floor Stands, Covers, Cords, etc. 



Inijlewood, Calif. 

Export Rep, at Ad. 
Auriema, Inc., 116 
Broad St.. N. T. C. 



Gears, speed reducers, sprockets, thrust bear- 
ings, flexible couplings, pulleys, etc. A com- 
plete line is carried in our Chicago stock. Can 
also quote on special gears of any kind. Send 
us your blue prints and inquiries. 

Write for Catalog No. 60 


769-773 W. Jackson Blvd. Chicago, III. 

^VVIRE <$ 

Quality wire for every type of hook-up 
"Alphex" a slip back braided hook-up wire made 

under a patented process. 

Alpha "HiTension" Wire (colored Rubber) 




520 Broadway, New York City 


Resistors QiJigffi 

Approved by leading engineers. 

Endorsed by test and experimental laboratories. 

Employed by scientific apparatus and precision 

instrument makers. 
Selected by discriminating receiver and amplifier 


Furnished in cartridge or pig- 
tail type, capacities ranging 
from 250 ohms to 10 meg- 
ohms, %, 1 and 2 watt types. 
Utilizes the famous metallized 

Write for New Illustrated Catalogue — or send us your Resistor Specifications — Samples for test will be 

furnished gratis. 

LYNCH MANUFACTURING CO., Inc., 1775 Broadway, N. Y. 

Projection Engineering, November, 1929 

Page 45 





HOTEL FORT SHELBY offers you accommo- 
dations of rare quality in an environment of 
restful quiet and comfort, although downtown 
Detroit — theaters, shops, wholesale district, 
rail and water transportation terminals — is 
practically at the doors. 

Here is every facility for making your stay a 
pleasant one — 900 reposeful, Servidor-equipped 
guest rooms, four excellent restaurants, and the 
thoughtful consideration of your interests in all 

Whether you choose one of the many excellent 
rooms at $3, $4, or $5 a day, or one of the 
higher-priced, especially large rooms or suites 
overlooking the city, or the river and Canadian 
shore, you will enjoy a particular sense of value 
in the Fort Shelby. Guests arriving by motor 
are relieved of the care of their cars by com- 
petent attendants. 

Tickets to theaters, concerts, sporting events, 
etc., reserved in advance upon request at the 
Fort Shelby. 

J. E. FRAWLEY, Managing Director 

Page 46 

Projection Engineering, November, 1929 

JANETTE Motor-Driven 
Speed Reducers 

Quiet, smooth-running machines consisting of motor 
and worm-gear reducer in one compact unit. Motor- 
end frame is cast integral 
with the gear housing, a 
unique construction conducive 
to compactness and perfect 
shaft alignments. Reductions of 
20 to 1 to 50 to 1. Motor speeds 
1750 or 1150. Sizes 1/30 to 
1/3 H.P. 

Write for 
Bulletin SR-529 



Transforms DC 
to AC to operate 
AC radios, elec- 
tric talking ma- 
chines, public 
address systems 
and motion pic- 
ture sound equip- 
ment in DC dis- 

Janette Mfg. Company, 

561 W. Monroe St., 


SJS g R B ' d 0- Real Estate 

149 Broadway Trust B , dg 


Speed Reducer 
specially design- 
ed for talking 
motion picture 
machines. Motor 
speed 1750 RPM : 
turntable speed 
33% IiPM. 

Specialists in 




Write Our Engineering Department 


— s * COMPANY ■* 



335 West Madison St., 
Chicago, 111. 








Standard with the ma- 
jority of manufacturers 
of Sound on Film 

There's A Reason 


1802 Grace St. 

Chicago, 111. 




AC Operated Speech 

Public Address. 

Mixing Panels. 

Power Supply Panels and 

Recording Amplifiers. 

55 East Wacker Drive, Chicago. 


Alpha Wire Co 44 

American Transformer Co. . .Third Cover 

Amplisound Systems, Inc 41 

Amrad Corp., The 5 

Arego Laboratories, Inc 44 

Best Manufacturing 
Burt Scientific Labs, 


Robert C . . 


Cameron Publishing Company 8 

Chicago Gear Works 44 

Clarostat Mfg. Co 37 

Crowe Name Plate & Mfg. Co 43 

Electro-Acoustic Products Co 46 

Elkon, Inc 6 

Enterprise Optical Company 

Back Cover 

Ferranti, Inc. 


G-M Laboratories, Inc 46 

General Amplifier Co 48 

General Industries Corp 44 

General Insulating & Mfg. Co 1 

International Resistance Co. 

Janette Mfg. Co 46 

Jenkins & Aadir. Inc 48 

Lynch Mfg. Co., Inc 44. 


Polymet Mfg. Corp 43 

Samson Electric Co Second Cover 

Shure Bros. Co 46 


Universal Microphone Co 44 

Weston Electrical Inst. Co 41 


Zapon Co., The. 

Projection Engineering, November, 1929 

Page 47 



(The subscription 
rate for individual 
subscribers is $2.00 a 

Will you not cooper- 
ate with us by classify 
ing subscriptions sent in 
as follows: 

(M) Manufacturer 

(Please check "M" if yon are an execu- 
tive, purchasing agent, production mana- 
ger, service manager, plant superintendent 
or foreman.) 

(E) Engineer 

(T) Technician 
(D) Distributor or 

(P) Projectionist 
(A) Theatre or Theatre 


Page 48 

Projection Engineering, November, 1929 

s fl$K 


is the manner in which many critics have 
expressed themselves after enjoying a sound 
demonstration with GENERAL AMPLI- 
FIERS and we believe this fittingly describes 
our devices. 

You will undoubtedly have to supply much 
sound apparatus and if your first installation 
meets with complete satisfaction you are in 
line for some interesting business. The am- 
plifier is the nucleus of all sound installations, 
so why not be safe with a GENERAL 
AMPLIFIER? We offer a laboratory-tested 
device and one guaranteed against defects 
in workmanship. All GENERAL AMPLI- 
FIERS possess unusually flat frequency char- 
acteristics and provide for the full undis- 
torted power output of the tubes employed. 

We maintain a free engineering service and 
are desirous of co-operating at all times. 
Consult us freely and write for Bulletin 
PE-1 today. 

Model GA-20 (Less Tubes) $225.00 


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Cambridge, Mass. 

565 Washington Blvd. 274 Brannan St. 

Chicago, 111. San Francisco, Cal. 

Jenkins 8C Adair Condenser Transmitter 


The type C condenser transmitter is the result of two years actual 
experience, during which these instruments have been used under all 
conceivable conditions, and in practically every part of the world where 
broadcasting or electrical recording is carried on. In addition to their 
excellence as pickup devices, they have proven to be extremely durable 
and rugged, and have shown a minimum upkeep cost. 

The type C transmitter is built for 6 or 12 v. A battery, and 180 v. 
B battery. The filament draws l A amp., and the plate. 3 to 6 M. A. 
The amplifier has a single stage and uses a standard tube. The trans- 
mitter unit is heavily gold plated, and the case is finished In dark 
brown enamel. 20 ft. of special double shielded cable with plug and 
socket are supplied. Our bulletin No. 6 describes this instrument in 


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Cable Address: 

Telephones : 
Keystone 213 

Acme Wire Products 

Parvolt Filter and By-Pass Condensers 
Coils — Magnet Wire Wound 

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For 25 years manufacturers and sup- 
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The Acme Wire Co. 


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52 Vanderbilt Ave. 

Branch Offices 

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Power Amplifier 

IN projecting sound to reach large assemblages of people in 
ball rooms, in the open air, or in rooms larger than those in 
the average home, the volume transmitted must be greater 
than is ordinarily attainable, but without the loss of tone, qual- 
ity, or fidelity of reproduction. 

The AmerTran Concert Hall Amplifier is distinguished for its 
exceptional purity of tone and exact reproduction of music and 
the speaking voice without distortion under greatly augmented 
volume. Of switchboard type construction with interchangeable 
panel sections, it requires a minimum of floor space. Being de- 
signed for either direct or remote operation the amplifier may be 
located at a distance from the speaker and from the radio tuner 
or other input source of audio frequency. Entirely AC operated; 
three stages of audio amplification; uses the new UX250 tubes. 

American Transformer engineers are ready to give you the 
benefit of many year's experience. Consult us freely — no obli- 
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(fT /?RITE for Bulletin 1077 containing complete 

yr technical data on the AmerTran Concert Hall 

Amplifier Type 2 5 A,approved by the Underwriters 


Licensed under patent of the Kadio Corporation of America and associated 
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MODEL}* ^" 












(Page Fourteen) 
By W. A. Morrison 


(Page Seventeen) 
By E. W. D'Arcy 


(Page Nineteen) 
By Jas. R. Cameron 


(Page Twenty-One) 
By Carl Dreher 


Sold only by subscription 
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World's Largest Talking Motion Picture Stage at the United Artists Studios 








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DETROIT, MICH.— N. Merion. SAN FRANCISCO, CALIF.— Jones Brothers Asbestos Supply Co. 

ST. LOUIS. MO.— L. Mundet & Son, Inc. 

"for clear, natural tones" 

Projection Engineering, March, 1930 

Page 1 

adds crowning touch to 
a famous hospitality 

012 Transformer 

The lure of mountain grandeur, framed in sunset gold, is 
enhanced by Pam amplified music at the Flintridge Bilt- 
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Wherever people gather to enjoy 
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rooms, PAM installations add 
pleasure and keep them in touch 
with the world. 

There are many opportunities for 
such installations right in your 
vicinity and each will bring other 

The 012 Variable Impedance Output 
transformer shown above has a pri- 
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pedance of any of our PAM amplifi- 
ers or its primary may be reduced to 

500 ohms. The secondary of this 
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pedance from 8 to 1000 ohms to suit 
most any condition. The 012 per- 
mits the use of two circuits of unequal 
impedance to be operated from the 
same PAM amplifier. 

A new 16-page bulletin giving me- 
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many new PAM Amplifiers will be 
sent upon receipt of 10 cents in 
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Main Office: 
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Factories: Canton and 
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Western Editor 

Evans E. Plummer 
Hollywood Editor 


Donald McNicol 

Associate Editors 

James R. Cameron 

Austin C. Lescarboura 

iiiii'iiiimiiiiiiii iiii'iiiiiiiiiiini: in iiiiiiiiiiiiiiiini n ii in : IfflllllU ill Ilium 11 mi iiniiiiiiiiiiiiiii i i i mini nimiiiiiiimi iniimii i niiiiim mi in iiiiiiiinim iimiiiii iiiiiimiiiiiiiiiiiii iiiiiiiiimni mini 

Vol. 2 

March, 1930 

Number 3 


Editorial 4 

Reproduction in the Theatre By S. K. Wolf 7 

Analysis of Camera Silencing Devices 13 

A Method for Estimating Audible Frequencies By W. A. Marrison 14 

Public-Address and Centralized Radio Systems, Part IV By E. W. D'Arcy 17 

Effect Lighting in Theatres By James B. Cameron 19 

Mobile Recording By Carl Dreher 21 

What the Motion Picture Means to the World By Will E. Hays 24 

Talkie Dominance a Tribute to Hollywood's Creative Minds By Wm. LeBaron 25 

Trade-Marks By Richards & Oeier 26 

D epartm ent s 

New Developments and News of the Industry 30 

Index of Advertisers 38 

Aviation Engineering 
Radio Engineering 
Projection Engineering 

Published Monthly by 

Bryan Davis Publishing Co., Inc. 

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Chicago Office — 333 No. Michigan Ave., Charles Farrell, Mgr. 

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San Francisco Office — 318 Kohl Bldg. I p,, n : t ,„j Rirrh 
Los Angeles Office— 846 So. Broadway f Cup,t ana Bircn 

Entered as second-class matter October 9, 1929, 
at the post office at Albany, N. Y., under the 
Act of March 3, 1879. 

52 Vanderbilt Ave. 
New York City 

Bryan S. Davis, 

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Advertising Manager 

Yearly subscription rate $2.00 in U. S. and 
Canada; $3.00 in foreign countries. 

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Projection Engineering, March, 1930 

Page 3 





Xe\tf* s "> 

>let^ on 



Page 4 


Projection Engineering, March, 1930 



March, 1930 





A S single purpose undertakings, perhaps 

/_\ only the railroads, shipping and the tele- 

/ % phone, in their beginnings, contained 

possibilities of exploitation comparable 

in magnitude to that which today may be 

visualized as the future of talking pictures. 

Even now talking pictures are credited with 
having added ten millions, or more, patrons 
weekly to the motion-picture theatres of this 
country alone. 

In New York City there are seventeen picture 
houses in the vicinity of Broadway and Forty- 
second Street. One of these seats six thousand 
persons four times each day, and another four 
thousand persons, grossing up to $117,000.00 
each week. Formerly ten of these were "legiti- 
mate" houses, including the Winter Garden, the 
citadel of pretentious musical shows. 

It is reported that at the present time there is 
in process in Hollywood a quantity of talking- 
picture entertainment far greater than at any time 
in the past, and it is said there is not a single 
project in production for the silent screen alone. 

A forthcoming Chaplin production, although 
scheduled to be put on without speaking parts 
in which the master of pantomine will talk, is 
reported to carry music parts and appropriate 
sound projections which will accentuate the art 
of the performer, and add to the realism of the 

It is well known that a time had arrived when 
the silent screen was in dire need of something in 
the way of innovation if the box-office attention 
of the public was to- be held to a sustaining extent. 
The commercial arrival of sound effects brought 
the tonic necessary tx> rehabilitate the screen 
amusement industry. 

Although the public has taken generously to 
the new talking-picture productions; getting along 
with them as they are, and making kindly allow- 
ances where allowances seem called for, the engi- 
neer and the projectionist know there is room for 

In what directions further advances will be 

made is at the moment speculative, but one thing 
is certain, and that is, that directly ahead there is 
much that will occupy the time and the ingenuity 
of the manufacturers, the engineers and the 
professional projectionists. The rewards will 
come to those who think and act with foresight, 
and constructively; those who have the genius to 
foresee wherein improvement is practicable, and 
who persist until betterment is realized. 


IT IS just about one hundred years since 
Professor Samuel F. B. Morse, at that time 
a portrait painter, witnessed Daguerre's 
photographic experiments in Paris. 
Daguerre had been experimenting in photography 
as early as the year 1826. 

It was in the year 1832 that Morse first dis- 
cussed his ideas about an electric telegraph, which, 
within twenty-five years thereafter, was to become 
a great industrial and social service. 

Recalling, in the year 1930, that the American 
inventor of the telegraph interested himself in 
duplicating the very first photographic experi- 
ments, one hundred years ago, is a reminder that 
throughout the intervening century of time the 
arts of electric communication and photography 
have maintained contact through the laboratory 
and service achievements of the engineers. 

In our times we find that the knowledge of the 
communication engineer — with radio and tele- 
phone experience — dovetails with and supplements 
the knowledge and experience of the photo-pro- 
jectionist in making possible the advanced art of 
talking pictures. 

While some of man's greatest works have 
reached fruition as a result of ultimate junction 
between supposedly unrelated lines of scientific 
endeavor, it is agreeable to realize that the 
modern art of projection of sound and light has 
reached its present eminence as the outcome of 
parallel contributions toward advancement — both 
arts fusing in synchronous fashion at a time when 
such fusion could serve a great purpose. 


Projection Engineering, March, 1930 

Page 5 


SCIENCE and art have gone far to take the gamble 
out of sound pictures. However, watch out for the 
joker! Uncertain line voltage can turn a succcessful 
house into a flat failure in a month's time. 

Don't take your 1 1 0-volt supply for granted. It may 
be anything from 85 to 1 40 volts. If high, your tubes 
will be short lived. If low, your tone and quality of 
reproduction will drop off, and so will your clientele. 

For sure-fire box office receipts there is just one form 
of insurance, namely, the 



Readily installed in input circuit. Requires no change 
in sound equipment. Inexpensive. Foolproof. Instantly 
compensates for line-voltage discrepancies. 


A heavy-duty resistor instantly 
adjustable to any resistance value. 
Holds settings. Available in 0-10, 
25 - 500, and 200 - 100,000 ohm 
ranges. Handles 250 watts. Pro- 
vided with extra long nipple for 
mounting on slate, marble, and, 
with special bracket, on Bakelite 
panel. Especially desirable for 

regulating input voltage, compen- 
sating for fluctuating line volt- 
age. Also available for all parts of 
sound reproducing system requir- 
ing fine resistance compensation, 
and for variable speed control of 
ventilating fans, blowers, projec- 
tion machine motors, and gener- 
ator fields. 

WRITE ^ or l' fer ature regarding this essential accessory. Better 

still, ask your supply house to show you the Super-Power 

Clarostat and explain how others in your territory are using it. 


Specialists in Variable, Fixed and Automatic Resistors 
296-7 North Sixth Street : : Brooklyn, N. Y. 

Page 6 

Projection Engineering, March, 1930 

uesswork i 



or scientific certaintyi 

in the correction of theatre acoustics 

COUND pictures present 
^ entirely new problems in 
acoustics. So thousands of dol- 
lars have been wasted in vain 
efforts to provide proper acoustics 
by unscientific methods. 

Stringing piano wires, re- 
plastering walls, redirecting air 
currents, remodeling beams, all 
these and many more have been 
attempted . . . with practically no 
effect upon the control of sound 

Acoustical engineers know that 
in 90% of all cases the need is for 
sound absorbing material to re- 
duce the reverberation created 
by too many hard surfaces on 
walls and ceilings. 

Acousti-Celotex with a sound- 
absorption efficiency as high as 
70% in Type BB, prevents the 
reflection of excess sound energy, 
reduces the period of reverbera- 
tion to within the proper range. 

This remarkable material 
comes in single, finished tiles, 
quickly and easily applied over 
existing surfaces. 

The needed amount of Acousti- 

Celotex and the proper location 
for its application can be readily 
calculated by exact scientific 

Every theatre requires indi- 
vidual treatment . . . because nu- 
merous factors, such as the depth, 
height and furnishings of the 
theatre enter into the problem. 

Simply submit all the details 
of your own sound-control prob- 
lems to the acoustical engineers 
of The Celotex Company for 
analysis and recommendation. 
Their services are yours without 
charge or further obligation. 

And the accuracy of their cal- 
culations have been checked and 
proven in hundreds of actual 


919 North Michigan Ave., 

Chicago, Illinois 

In Canada: Alexander Murray & Co., Ltd., 

Mills: New Orleans, Louisiana 

Branch Sales Offices in many principal cities 
(See telephone books for addresses) 

Acousti-Celotex is sold and installed by approved 
Acousti-Celotex contractors 

The word 


(Reg. U. S. Pat. Off.) 

is the trademark of and indicates manufacture by 

The Celotex Company, Chicago, Illinois 



Projection Engineering, March, 1930 

Page 7 

Reproduction in the Theatre 

By Western Electric System 
By S. K. Wolf* 

THE addition of sound to motion 
pictures more than doubled the 
amount of projection equipment 
necessary in the theatre. The 
images on the film are after all just 
translucent miniatures of what is to be 
shown on the screen. The sound 
source on the other hand is either a 
tiny scratch on a wax disc or an odd 
looking border along the film. In both 
cases a delicately elaborate arrange- 
ment of electrical machinery must in- 
tervene before the sound locked in the 
film or disc by the recording process 
can be brought to new life. 

Three essential elements make up a 
reproducing system. They are : 

(1) A pickup or reproducer. 

(2) An amplifier. 

(3) A loudspeaker or receiver. 

The function of the reproducer is to 
transform the sound record into elec- 
trical energy. The function of the am- 
plifier is to magnify the infinitesimal 
electrical energy to the desired value. 
The function of the loudspeaker is to 
transform this amplified electrical en- 
ergy into acoustic energy and to dis- 
tribute the acoustic energy or sound 
throughout the theatre or auditorium 
wherein it is being produced. 

At the present time there are two 
types of sound recording used com- 
mercially. These are known as the 
film and the disc methods. The only 
essential difference between the sys- 
tems used for reproducing film and 
disc records is in the pickup apparatus. 

Fig. 1 is a schematic diagram show- 
ing the general layout of a sound re- 
producing system. You will note that 
provisions are made for reproducing 
both film and disc records, also that 
two machines are equipped, making in 
all four pickup devices. Obviously two 
machines are necessary to the con- 
tinuity of the picture and sound re- 
production. Provision is also made for 
selecting either the film or the disc 
pickup in Machine No. 1 or Machine 
No. 2. The next piece of apparatus in 
the circuit is the fader, the function 
of which is to control the volume of 
sound energy from this system. Fol- 
lowing the fader is a switching panel 
which permits use of non-synchro- 
nous reproduction as well as synchro- 
nous reproduction. After the switch- 
ing panel are the amplifiers, a more de- 
tailed discussion of which will fol- 
low. The next element in the circuit 
is an output control panel, the func- 
tion of which is to join the amplify- 
ing units with the loudspeaker or re- 
ceiver units. The receivers, as has 

t A paper included in the Technical 
Digest of the Academy of Motion Picture 
Arts and Sciences. 

* Theatre Acoustics Engineer, Electrical 
Research Products, Inc. 

been stated, serve to transform the 
amplified electric energy into acoustic 
or sound energy. 

Disc Reproducer 

In elaborating on the above descrip- 
tion, let us discuss first the method 
known as disc reproduction. In disc 
reproduction a magnetic type of re- 
producer is used almost exclusively. 
This type of reproducer consists of a 
stylus connected to an armature of 
high permeability which is located 
within a small coil. In operation the 
stylus attached to the armature vi- 
brates as a needle follows the grooves 
on the sound record. The movement 
of the armature between the poles of 
the magnet which surrounds the arma- 



The separation between these lines de- 
pends upon the frequency of the sound 
while the contrast between the light 
and dark parts represents the loudness 
or intensity. In the variable area 
method the sound record is made by 
varying the width of the dark portion 
of the sound track. While with this 
variable area method the unmodulated 
track consists of a dark and a light 
band each one-half the width of the 
sound track, in the variable density 
method unmodulated track appears a 
uniform gray over the entire width. 

In transforming the film record into 
electric energy the essential elements 
required for this transformation con- 
sist of an exciting lamp, a lens system 
and a photoelectric cell. 

























BOX —> 



Fig. 1. Schematic diagram of a sound reproducing system. 

ture causes a variation in magnetic 
lines of flux and a voltage with cor- 
responding variations is induced in the 
coil. This induced voltage is an elec- 
trical image of the sound record. 

A section of this type of reproducer 
is shown in Fig. 2. This is a simple 
schematic diagram which will serve to 
illustrate the fundamental electric 
principle involved in the transforma- 
tion of the sound record into an elec- 
tric image of the record. 

Film Reproducer 

With the optical or film record the 
situation is somewhat different. In 
this case the pressure variations 
caused by the sound have been trans- 
formed into a photographic image on 
the edge of the film. In the variable 
density film record this image takes 
the form of alternate light and dark 
lines running across that portion of 
the film reserved for the sound track. 

Fig. 3 is a schematic diagram of the 
sound head, parts of which will be de- 
scribed later in detail. It is evident 
from the relative location of appara- 
tus as shown in Fig. 3 that it is not 
feasible to print the film sound record 
directly beside the picture to which 
it applies. The sound track is printed 
approximately 15 inches in advance. 
This allows some slack between the 
sprocket which carries the picture 
with an intermittent motion before 
the picture projection lens and the 
sprocket which must carry the sound 
record with a uniform motion in front 
of the photoelectric cell. Special pre- 
cautions are necessary to prevent 
vibrations and speed fluctuations, due 
to either a varying supply voltage or 
a varying load, from affecting the uni- 
formity of rotation of the sound 
sprocket. The speed of the driving 
motor is automatically controlled as 
described in this paper under the head- 

Page 8 

Projection Engineering, March, 1930 






Fig. 2 Schematic diagram illustrat- 
ing electrical principle. 

ing" Maintaining Synchronism. A 
mechanical device is also interposed 
between the sound sprocket and the 
rest of the moving equipment of the 
projector so that no abrupt change of 
speed will be transmitted to the sound 

Fig. 4 shows the exciting lamp and 
the lens relative to the film plane. 
The light from the exciting lamp is 
focussed on to the film as a very nar- 
row beam one mil in width. It is 
necessary that this beam be very nar- 
row as the highest reproducible fre- 
quency depends upon the speed of the 
film and the narrowness of the light 
beam falling on the sound track. The 
photoelectric cell on which the light 
falls after passing through the sound 
record is shown in Fig. 5. 

Film reproduction is made possible 
through the use of this photoelectric 
cell or one having similar charac- 
teristics, that is, a cell capable of 
emitting electrons at a rate propor- 
tional to the incident light within cer- 
tain predetermined limits. This cell 
consists of two electrodes, one a photo- 
active metal and the other the sole 
function of which is that of an elec- 
tric conductor. The photoactive metal 
most used for the purpose of sound 
reproduction is potassium. However, 
other alkali metals have been used. A 
polarizing voltage is placed across the 
terminals of the photoelectric cell 

through such a high resistance that in 
operation there is obtained from the 
cell a voltage across this resistance 
which is proportional to the incident 
light. This cell may be thought of 
simply as a resistance which varies 
directly with the quantity of light fall- 
ing on the cell. 

The photoelectric cell circuit is 
shown in Fig. 6. In a high impedance 
circuit such as this, local interference, 
sometimes termed static, is readily 
picked up and if not guarded against 
will produce serious distortion in re- 

Since the energy level is so small, 
induced current may be appreciable in 
comparison to the sound currents 
themselves. In addition, there are 
other electrical effects which may 
create some distortion. Because of the 
low level of this power, it would be 
dangerous to transmit it any great 
distance before it has been amplified. 
Therefore, an amplifier (called a PEC 
amplifier) is placed immediately ad- 




Fig. 3. Sche- exciting lamp 

matic layout 

of sound head. STRIPPER 

tions are taken to insure against me- 
chanical shock by carefully suspending 
the tubes of the amplifiers. The out- 
put of this amplifier is approximately 
the same as that of the magnetic re- 
producer used in disc reproduction. 
This will permit the remainder of the 
reproducing system to be used inter- 
changeably between film and disc 
pickup. As shown in Fig. 1 this 
change is facilitated by means of a 
transfer switch. 


The energy produced by the pickup 
apparatus is not of sufficient magni- 
tude to fill large spaces if it were 
transformed into acoustical energy. 
For that reason it is necessary to 
amplify the electric power of the 
pickup apparatus. The apparatus re- 
quired for this amplification is a very 
important part of the equipment and 
must be carefully designed in order 
to insure against distortion of the ori- 






jacent to the photoelectric cell circuit 
to amplify the power to a level at 
which it can be safely transmitted. 

This amplifier increases the photo- 
electric cell output approximately 50 
decibels or a power ratio of 100,000 
to 1. The photoelectric cell and am- 
plifier are encased in a heavy metal 
box which is fastened to the frame 
of the projector and the frame is 
carefully grounded. Further precau- 


■< 3(l>.l<3fr> j 



\ SLIT gg&Si'i- WIDE x 3/ 16" LG. 

APPROX. 4 1/4" 



Fig. 4. Light 
from exciting 
lamp focused 
on film as 
beam one mil 


ginal power obtained from the sound 

Amplifiers have been designed in 
different sized units so that a selection 
of units may be obtained for the 
proper volume of sound for the widely 
varying size of theatres. In Fig. 7 
are shown three of the amplifiers used 
in the Western Electric sound projec- 
tion system. These amplifiers may be 
classified as Gain Amplifiers and 
Power Amplifiers. 

The gain amplifier is used for the 
purpose of amplifying the small elec- 
tric power obtained from the magnetic 
pickup or from the photoelectric cell 
amplifier to a level suitable for operat- 
ing the power amplifiers, which ampli- 
fiers are to drive directly the loud- 

In a house of about 1200 seats, that 
is about 175,000 cubic feet, it is only 
necessary to use the gain amplifier and 
one power amplifier. In houses up to 
500,000 cubic feet or from 2,000 to 
3,000 seats the gain and two power 
amplifiers are used. In houses such 
as Boxy's with 6,000 seats and a mil- 

Projection Engineering, March, 1930 

Page 9 

lion cubic feet power amplifiers are 
added in multiple. In the new mu- 
nicipal auditorium at Philadelphia 
there are about 24 of these amplifiers. 

The first or gain amplifier in the 
wall panel is identified as the 41-A 
unit in the Western Electric System. 
Fig. 8 is a schematic diagram of the 
41-A unit, a three-stage resistance 
coupled amplifier. The filaments in 
the tubes of this amplifier are con- 
nected in series and energized from a 
twelve volt battery supply drawing 
normally one-fourth of an ampere. 
The voltage supply for the plate cir- 
cuit of this amplifier is obtained from 
the amplifier following, which has its 
own rectifier. This plate potential is 
obtained at 390 volts and is reduced 
by resistances placed in the plate cir- 
cuit of each stage so that the voltage 
of the plate of each tube is kept at 
approximately 100 volts. In the cir- 
cuit with these resistances are coils 
and condensers to smooth out the 
rectified voltage supplied to these sen- 
sitive first stages. 

Even the slightest knock or jar of 
the tubes is converted into electrical 
impulses which are transmitted 
through the system to the loudspeakers 
where they appear as grating sounds. 
To prevent disturbances, the three 
vacuum tube sockets are mounted on 
a piece of sponge rubber which is 
fastened to a heavy steel plate and 
this plate is likewise suspended on a 
sponge rubber mounting. This sus- 
pension method is the mechanical 
analogue of the electric filters used to 
quiet the B supply on the amplifier 
systems, and represents a very efficient 
means of insulating the tubes from 
mechanical vibrations. 

In order to control the gain or am- 
plification of the system, a potentio- 
meter is placed in the grid circuit of 

Fig. 5. Photoelectric cell. 

the first tube of the 41-A unit. This 
affords a gain control of 66 decibels in 
steps of three decibels each. A second 
means of controlling the gain of this 
amplifier is put in the grid circuit of 
the second tube. This gives an addi- 
tional gain of 14 decibels. Gain con- 
trols could be put on the power ampli- 
fiers as well as on the 41-A unit, but 
this is not considered necessary. This 
gain control through the potentiometer 

should not be confused with the fader. 
The potentiometer is ordinarily set at 
the time of installation. 

Each of the power amplifiers con- 
sists of a single stage circuit known 
as a "push-pull" circuit. This is shown 
in Fig. 9. The power amplifiers 
operate entirely from alternating cur- 
rent. The 42-A and 43-A amplifiers 
shown in Fig. 7 consume approxi- 
mately 80 watts and 300 watts re- 
spectively. The amplifiers each make 
use of four tubes, two as amplifying 
tubes and two as rectifying tubes. The 
two rectifying tubes supply a plate 
voltage of 400 volts in the case of the 
42-A amplifier and 800 volts in the 
case of the 43-A amplifier. No means 
are provided for controlling the gain 

other types of receivers, but the above- 
mentioned type has to date best ful- 
filled the requirements of talking pic- 
tures. The operations of these electro- 
dynamic receivers depend upon the 
force which exists between a coil of 
wire carrying a current and a sur- 
rounding uniform magnetic field. The 
magnitude and direction of this force 
depends upon the magnitude and di- 
rection of the current flowing in the 
coil, and upon the magnitude and di- 
rection of the uniform external mag- 
netic field. Hence, as the speech cur- 
rent is applied to this coil it will tend 
to move in and out in such a manner 
as to follow the wave shape of the cur- 
rent, which completes the last step in 
recreating the original sound. 

Fig. 6. Circuit 
including pho- 
toelectric cell. 






of these amplifiers. These amplifiers 
are operated by means of a three-posi- 
tion snap switch which controls the 
a-c. supply. In starting the switch 
is turned to the first position which 
lights the filaments only. After they 
have had time to become heated, the 
switch is turned to the next position 
which supplies the plate voltage, mak- 
ing the amplifier ready for operation. 
This procedure in starting reduces the 
strain on the vacuum tubes which 
would occur if a high voltage were ap- 
plied while the filaments were still 

The 42-A amplifier is capable of am- 
plifying the power it receives approxi- 
mately 325 times, which is equivalent 
to 25 decibels. The 43-A amplifier has 
a power amplification of approximately 
36 times or 15 decibels. The 41-A, 
42-A, 43-A combinations of amplifiers 
are capable of a power amplification 
of 100,000,000 times or 80 decibels. 

For some houses, that is up to about 
1.200 seats, the 42-A amplifier will de- 
liver sufficient power without distor- 
tion to get satisfactory results. In 
larger houses one or more 43-A ampli- 
fiers may be necessary, the number de- 
pending upon the size of the house. 

Loudspeakers or Receivers 

After the sound has been taken from 
the record and transferred into elec- 
trical power and amplified, it is then 
led to the loudspeakers which convert 
it into sound. The types of receivers 
most used at the present time for 
talking picture work are the electro- 
dynamic coil type. There are many 

The receiver used with the Western 
Electric system is known as 555-W. 
It consists of a duraluminum dia- 
phragm. The diaphragm is made of a 
single piece of sheet aluminum alloy 
0.002 inches thick. This diaphragm 
(A) is shown in Fig. 10. To it is 
rigidly mounted a flat coil ( B ) of 
aluminum wire or ribbon 0.015 inches 
wide and 0.0002 inches thick, wound on 
edge. A thin coat of lacquer serves to 
insulate the turns from each other. It 
is the speech current circulating in 
this coil interacting with the magnetic 
field which forces the diaphragm in 
and out. 

The receiver has been so constructed 
that the diaphragm vibrates as nearly 
like a rigid plunger as possible. This 
is accomplished by so shaping the 
center portion of the diaphragm that 
it is relatively stiff compared with the 
edge. Furthermore the coil which 
drives it is fastened around the out- 
side of the stiffened central portion. 
The coil which is rigid and very light 
is made self-supporting. This form of 
mounting enables the coil to radiate 
heat readily, and therefore permits a 
large power input to the receiver with- 
out overheating. 

The outstanding feature of this type 
of receiver is the high efficiency with 
which it converts electric energy into 
acoustic energy. In experimental 
models efficiencies as high as 50% 
have been realized. When you con- 
sider that a receiver of 100% efficiency 
would result in an increased sound in- 
tensity of three decibels, which is only 
a comfortably perceptible difference, 

Page 10 

Projection Engineering, Mca-ch, 1930 

it is not likely that much economy 
would be gained from higher effi- 

This type of receiver, when used, is 
attached to a horn which partially 
isolates a column of air from the sur- 
rounding medium. This column of air 
affords an acoustic coupling between 
the receiver and the space in which 
the sound is to be reproduced. 

The horn is designed in such a way 
as to avoid interference between air 
waves as they pass through the cham- 
ber and the throat of the horn. The 
horn used is shown in Fig. 11 ; its de- 
sign and construction is referred to 
technically as "exponential," which 
qualifies its shape. 

Maintaining Synchronism 

Synchronization between sound 
records and photoelectric records is an 
inherent requirement of sound pic- 
tures. In projection this is usually 
accomplished by mechanically coupling 
the picture projection machine with 
the sound recorder. Synchronization 
in itself is not sufficient, however, for 
there is still the problem of speed con- 

Since musical pitch depends upon 
the frequency, it is necessary in re- 
producing music with fidelity of pitch, 
that the sound record be run at iden- 
tically the same speed as that at which 
it was made. To accomplish this, some 
reproducing systems make use of a 
synchronous motor or certain types of 
induction motors whose speed charac- 
teristics are inherently constant under 
certain given conditions. However, 
variations of load, supply voltage and 
frequency may produce noticeable 
variations in pitch of the reproduced 
sound. A trained musical ear may de- 
tect pitch changes caused by speed 
variations greater than one-fifth of one 
per cent, particularly if these occur as 
fluctuations. The ordinary untrained 
ear may detect changes of less than 
one per cent. To further insure 
against such discernible changes in 
pitch, the Western Electric system 
makes use of a device known as a 
motor control box which maintains a 
motor speed regulation of one-tenth of 
one per cent, despite the ordinary 
variations of power supplies. 

The motor control box furnishes an 
electric method of accurately control- 
ling the motor speed. Its contents are 
somewhat elaborate and need not be 
described in detail for the purposes of 
this paper. A brief statement of its 
bridge circuit is given below : 

Fig. 12 shows the governing system. 
The circuit is a special bridge circuit. 
One arm of the bridge is made up of 
a fixed inductance L and fixed con- 
denser C in series. The valves of C 
and L are such that they tune the cir- 
cuit at 720 cycles. Another arm of 
the bridge is pure resistance D with an 
impedance equal to the impedance of 
the capacity and inductance at 720 
cycles, hence the ratio of the resist- 
ance D to C and L is unity at this 























Fig. 7. Panel layout of three gain and power amplifiers. 

frequency. The other two arms of the 
bridge circuit is the primary of T 4 
divided at its half tap. A 720 cycle 
potential is supplied from a small al- 
ternator when it is driven at 1200 
R.P.M. This alternator is directly 
connected to the shaft of the main 
driving motor. When the speed is less 
than 1200 R.P.M. the applied potential 
across the bridge circuit is less than 
720 cycles, hence the current in C is 
leading due to the predominance of 
the condenser, and if the frequency 
goes over 720 cycles, the current is 
lagging due to the predominance of 
inductance. Hence with a change of 
speed there is a change of 180° phase 
from less than 1200 R.P.M. to more 
than 1200 R.P.M. This shift of phase 
changes the potential of the grid of 
V* relative to the plate from negative 
to positive or vice versa, and thereby 
causes a relatively large change of 
plate current. This current flowing 
through resistance Ri causes a corre- 
spondingly large change in the grid 
potentials of Vi and V=. Thus it is 
that a change of speed will either in- 
crease or decrease the current supply 
from Vi and V 2 . This current flows 
through a winding which is on the 
same iron core as Lt. With increasing 

current from these two tubes, the 
magnetic flux in the iron core will in- 
crease to saturation and the imped- 
ance of Li decreases. The torque of 
the driving motor varies inversely 
with the impedance of the rotor circuit 
and hence with the impedance of In. 
Therefore, with an increase of current 
from Vi and V 2 the reactance of Li 
decreases and the motor will speed up. 
Likewise a shift of phase of 180° will 
cause a lesser current from Vi and V» 
and cause the reactance of Li to in- 
crease and the motor to slow up. To 
keep the motor speed more constant 
an additional network of R 2 , Ra, Ri 
and C 2 is added in such a manner that 
a change of potential across R 2 feeds 
back to the grid of V* and thereby 
gives the circuit additional regulation. 

V 3 is a rectifier tube and furnishes 
direct current to the field of the 720 
cycle generator. 

By these means the motor speed is 
kept, under ordinary conditions, to 
within two-tenths of a per cent 

Switch Si when closed toward the 
right will make the motor run un- 
regulated except for the hand adjusted 
potentiometer Pi and the motor speed 

Projection Engineering, March, 1930 

Page 11 

-JMt l**#VT IRAN} »•-* POTCWT 


TO «ro»M rw>M 

200 0MM1 

Fig. S. Diagram of a three-stage resistance coupled amplifier. 

may be adjusted to 
operator might want. 

whatever the 

Volume Control 

It is necessary to have some means 
of varying sound levels in theatres, 
first because of the variation in sound 
energy requirements in theatres, sec- 
ond because of the variation in levels 
of recorded sound, third because of the 
variation in the size of the audiences 
and fourth the desirability of level 
control during reproduction for the 
purpose of emphasis. 

Most reproducing systems make use 
of two means of controlling sound 
levels. The first of these methods is 
the use of the gain control, with which 
the gain amplifier is equipped. The 
other is the use of an attenuating de- 
vice known as the fader, which is 
usually connected electrically just 
ahead of the gain amplifier. The first 
method is generally used to adjust the 
amplifier system to the requirements 
of the particular theatre, while the 
second method is used by the operator 
during the show. 

Causes of Distortion and Factors 
Affecting the Fidelity of Repro- 

Factors causing distortion in a re- 
producing system may be classified 
under three heads. First, those affect- 
ing the response at various frequencies 
(called frequency characteristics) ; 
second, those which cause the type of 
distortion known as non-linear ; third, 
those which cause the addition of ex- 
traneous noises. In the case of the 
Western Electric system, if the ap- 
paratus is properly maintained and 
operated, the frequency characteristic 
is quite uniform from slightly below 
60 cycles to somewhere above 5,000. 

The type of distortion known as non- 
linear is the type which occurs when 
an amplifier or other part of the sys- 
tem is overworked. Such distortion 
may get into the reproduction in the 
theatre from one or more of the fol- 
lowing causes : improper printing and 
developing of the sound track on the 

film or badly worn disc records, too 
low a charging potential for the photo- 
electric cells, too low filament currents 
or plate voltages on the amplifiers, in- 
sufficient magnetizing current on the 
receivers and other similar causes. 

The extraneous noises which usually 
tend to be introduced by mechanical 
vibrations and interference from the 
power supply circuits, have been re- 
duced to a minimum by the use of 
shielding and of both mechanical and 
electric filters in the design of the ap- 
paratus. Very little extraneous noise 
will be introduced in the film ma- 
chine, provided the sprockets are kept 
in proper alignment and the film gate 
is kept clean. 

233 4 

Poor maintenance may result in de- 
velopment of bad contacts, faulty tubes 
and other similar troubles. These 
troubles usually result in causing one 
or more of the above types of distor- 
tion to be introduced into the repro- 
duced sound. 

Portable Sound Projector 

Fig. 13 is a photograph of the West- 
ern Electric 202-A projector, a portable 

This projector has a maximum 
throw of sixty feet. The maximum 
picture size is seven feet by eight feet. 
The apparatus is suitable for audi- 
ences up to 800. 

In the upper left-hand corner of Fig. 
13 may be seen the 1000-watt in- 
candescent projecting lamp, with its 
mirror and condensing lens. Directly 
to the right is the projector with the 
orifice through which the beam is pro- 
jected discernible under and adjacent 
to the lifting handle on the outside 
of the case. Directly under this is 
located the photoelectric cell and be- 
tween this cell and the center of the 
case is located the sound gate, lens 
assembly and exciting lamp. Only one 
magazine is used. The two reels are 
placed on the same shaft with a spacer 
between them, the take up reel in the 
inner position. The film is threaded 
from the outside reel up through the 
outer feed sprocket in a large loop 
which passes over the top of the pro- 
jector down through the light gate 
over the intermittent sprocket, then 
over the inner feed sprocket, down 
through the sound gate, over the sound 
sprocket and into the take-up reel. It 



Fig. 9. Circuits of push-pull power amplifier. 

Page 12 

Projection Engineering, March, 1930 

Fig. 10. 

Section of No. 

555 -W 

thus leaves the magazine and describes 
a loop through the apparatus back to 
the other reel in the same magazine. 
The preliminary amplifier is located 
behind the magazine in this illustra- 
tion and consists of two stages 
mounted on a spring suspension. 

Fig. 11. Ex- 
ponential horn, 
designed to 
avoid interfer- 


Fig. 12. Circuits of governing system on bridge principle. 

First Talking Picture Telling 
the World Hoiv It Is Done 

"Finding His Voice," Western 
Electric's 1,000 foot film which 
is the first talking picture telling 
how talking pictures are made, is 
completing its first Broadway 
showing, a week's run at the 
Capitol. The picture was booked 
after a screening by Manager 
Emmett and the audience reac- 
tion has justified the feeling that 
Broadway patrons are intensely 
interested in seeing and hearing 
how films get their voice. 

"Finding His Voice" explains 
in cartoon style the intricacies 
of talking picture production, il- 
lustrated in a way to make the 
process clear to any layman. 

Means are provided to lock this sus- 
pension during transportation. The 
motor is seen in the lower left corner 
of the case. The drive is by means of 
stepped pulleys and a round fabric belt 
to allow for adaptation for either 50 
or 60 cycle current supply. To the left 
of the motor may be seen the control 
panel which is equipped with meters 
and rheostats for proper control of 
filament supply to exciting lamp and 
amplifier filaments, and with proper 
volume control. 

The final amplifier is furnished in 
another trunk. This amplifier is a 
standard small size theatre equipment. 
A screen trunk is supplied with a 
collapsible rack to support the screen 
and a horn trunk furnishes the sup- 
port for the horn in the proper rela- 
tion to the screen. 


— In the April issue of Projection 
Engineering : Dr. Pitken's story about 
the psychology of sounds. 

Fig. 13. W.E. 

202-A portable 



Projection Engineering, March, 1930 

Page 13 

Analysis of Camera Silencing Devices 

Academy of Motion Picture Arts and Sciences Committee Submits 


A DETAILED analysis of the ef- 
ficiency of sixteen different 
camera silencing- devices used 
in the recording- of talking pic- 
tures, is embodied in a report just an- 
nounced by Irving Thalberg, chairman 
of the Producers-Technicians Joint 
Committee of the Academy of Motion 
Picture Arts and Sciences. 

The analysis is the result of tests 
conducted to ascertain features to be 
incorporated in a standard and simpli- 
fied camera silencing device. Further 
investigation is now being arranged. 

The research is under the direction 
of a sub-committee, composed of H. G. 
Knox, vice-president, Electrical Re- 
search Products, Inc., and F. M. Sam- 
mis, general Pacific Coast representa- 
tive for RCA Photophone, Inc. 

Sound booths large enough to hold 
both camera and cinematographer 
were not included in the tests which 
were limited to "blimps," "bungalows" 
and camera blankets. 

The research, it is stated, is not 
aimed at an attempt for camera re- 
design, but is concerned only with mak- 
ing possible the creation of a silencing 
device of maximum efficiency. 

Among preliminary recommendations 
are: Motors should be mounted as an 
integral part of the camera so that any 
external silencing device will be effec- 
tive for both. 

Devices for coupling the motors to 
the cameras, including- cables and 
gears, should be improved to provide 
more quiet operation. 

The type of tripod used does not 
seem to have much effect on the noise. 
On the basis of these preliminary re- 
sults, the use of a heavy steel tripod 
seems unnecessary in so far as sound 
insulation is concerned. Covering the 
tripod with blankets seems to help in 
reducing any tendency to vibrate. 

Photographing through glass reduces 
the noise transmitted through the 
silencing device. 

The amount of noise transmitted 
through the silencing- device appeared 
to be nearly independent of the direc- 
tion of the pickup device from the 

Rough quantitative observations in- 
dicate that the various blimps and 
bungalows absorb more high than low 

The camera, mechanism should be 
properly serviced and maintained so 
that it will remain quiet. Some 
cameras tested were noisier than others 
of the same make. 

Soundproof rooms in the Hollywood 
laboratory of Electrical Research Prod- 

ucts, Inc., were used for the tests. Fig. 
1 shows the arrangement of the camera 
and microphone. 

The microphone was suspended at 
normal camera height and placed as 
shown, 6 feet from the center of the 
tripod supporting the camera. Since 
this setup was used for all of the tests, 
the results are directly comparable 
from the point of view of sound in- 
sulation for the various camera sil- 
encing devices. 

Fig. 2 presents a schematic diagram 
of the circuit employed, similar to a 
standard recording channel, with the 
introduction of an accurate variable 
attenuator. The mixer and volume 
control dials were not used for the 
quantitative measurements, but were 
set on their minimum loss positions. 

The method used in determining the 
noise from a given camera, and as- 


Fig. 1. Relative positions of 
camera and microphone. 






Fig. 2. Sche- 
matic of cir- 
cuit including 
variable atten- 

0-70 db 




soeiated motor, was to measure the 
noise with the volume indicator. A 
variable attenuator was adjusted to 
give standard deflection to the volume 
indicator, sufficient gain being pro- 
vided by the amplifiers so that a 
definite attenuator reading could lie 
obtained even for a quiet room. The 
amplifier gains and volume indicator 
readings were kept constant through- 
out the series of tests. The sound 
insulation value of the device under 
test, whether it be a blanket, bag, com- 
position bungalow -or metal housing, 
will then be the difference between the 
attenuator readings for the camera and 
motor without and with the silencing 
device. Room noise during the tests 
was in all cases 5 to 10 db. below the 
quietest camera condition measured. 

As a means of determining roughly 
the relation between the sound inten- 
sity obtained from the cameras with 
their silencing devices and the sound 
level occurring under talking-picture 
conditions, a few measurements were 
made of normal speech and whispering 
at a distance of six feet from the 
microphone, that is, from the tripod 
position. The noise from many of the 
cameras tested with the better sil- 
encing devices gave a sound intensity 
of the same order of magnitude as a 
loud whisper, and could not therefore 
be used for very quiet scenes, unless 
the camera is some distance from the 
microphone. Since this condition ex- 
ists, many of the cameras tested must 
be used at least ten to fifteen feet from 
the microphone in order that the cam- 
era noise will not be objectionably 

The use of heavy steel tripods does 
not seem to contribute to noise reduc- 
tion. Wrapping blankets around the 
tripod legs seems to reduce the noise 



I7B & 9A 



Page 14 

Projection Engineering, March, 1930 

picked up by the microphone in some 
cases. It is probable that excessive 
vibration in a camera caused by a de- 
fective mechanism, loose film in the 
spools in the magazines, or loose gears 
in the motor drive, will be more readily 
transmitted to the legs and so cause 
trouble. The effect of insulation of 
the tripod head has not been definitely 

It should be kept in mind that elab- 
orate silencing devices are not required 
in all of the places where the camera 
is used, the report points out. For out- 
door shots, crowd sequences, musical 
sequences, in fact most scenes where 
the camera is quite far from the micro- 
phone, only a moderate degree of sound 
insulation is required. Pre-recorded 
and silent shots, of course, require no 
sound insulation. 

The following table is a partial sum- 
mary of the data collected. It will 
indicate the wide variation in ef- 
ficiency of silencing devices now being 
applied to cameras. 

Column 1 is a brief description of 
the nature of the silencing equipment. 

Column 2 shows how much louder 
or softer the noise of the uncovered 
camera was than average whispering. 

Column 3 shows the sound insulating 
ability in db. of the various devices 

Column 4 shows how many db. louder 

or softer is the noise of the camera 
enclosed in its protecting device than 
average whispering. 

The plus sign indicates that the noise 
as shown in the table is louder than 

normal whispering, whereas the minus 
sign indicates that it is weaker than 
whispering. The zero value indicates 
that it is the same value on the average 
as whispering. 


1 2 3 4 5 
Rigid composition blimp set on table (Flexible cable 

inside blimp) +s 19 — 11 Z 

Blanket hood and blankets over tripod +11 12 — 1 W 

Special capok blimp ; no blankets +13 15 — 2 W 

One-piece cast aluminum bungalow +15 19 — 4 Z 

Rigid composition blimp +15 15 Z 

Papier mache blimp +15 18 — 3 Z 

Rigid composition blimp +13 14 — 1 W 

Rigid composition blimp +20 12 + 8 W 

Rigid composition blimp +6 10 — 4 W 

Semi-rigid multilayer bag +6 11 — 5 W 

Heavy blanket thrown over camera (open at both 

front and back) +5 2 +3 W 

Old bag : Light, blanket around tripod +10 9 + 1 W 

New bag : Heavy, blanket around tripod +10 10 W 

Special bag : Heavy +10 14 — 4 W 

Metal bungalow +11 17 — 6 Z 

Semi-rigid zipper blimp ; blankets around tripod +9 11 — 2 Z 

Rigid composition blimp +20 15 + 5 W 

The data indicated that some of the studios, while having less effective 

sound insulating equipment, had taken greater pains in the maintenance and 

care of their cameras and drive mechanisms, so that the low volume of sound 

is due to the camera and drive making less noise to start with. 

Column 5, Tripod : 
Standard wood (W). 
Special (Z). . 

A Method for Estimating Audible 


Use of Musical Intervals to Estimate Audio Range 
By W. A. Marrison 

IT is often desirable when making 
calibrations and other frequency 
measurements to be able to es- 
timate the frequency of a tone 
without the aid of elaborate standards 
or measuring apparatus. By a simple 
use of musical intervals which nearly 
everyone can learn easily to recog- 
nize, any frequency in the range from 
approximately 50 to 4000 cycles 
( rough tly 7 octaves) can be estimated 
by ear with considerable accuracy, 
given a single frequency in this range. 
The single frequency may be ob- 
tained from a fork, reed, or pitch 
pipe. Some people with an "absolute 
ear" can recognize certain pitches 
without any auxiliary means ; violin- 
ists frequently can tune their instru- 
ments to standard pitch without any 
outside aid. In the absence of any of 
these aids, however, one can have an 

* From Bell Laboratories Record, Decem- 
ber, 1929. 

approximate standard in his own 
voice or whistle. The lowest notes 
one can sing and whistle are quite 
definite and can usually be relied upon 
to within 10 per cent. These lowest 
notes may conveniently be used as ref- 
erence standards in terms of which 
the frequency of any other musical 
tone may be estimated. 

For men, the lowest singing tone 
will range with individuals from 60 
to 120 cycles and the lowest whistle 
from 500 to 700 cycles. For women 
the singing tone is approximately one 
octave higher. One may readily cali- 
brate his "standards" by means of a 
piano with the aid of the accompany- 
ing chart in which the frequency of 
every note of the equally-tempered 
scale is given in a range of eight oc- 
taves. The note known as middle 
"C" has a frequency of 258 cycles. 
One must be sure, in making this 
test, that the sung tone is identified 

with the correct piano note, and not 
with one an octave higher or lower. 
Strange as it may seem, one who has 
had some experience with singing is 
likely to make this mistake since men 
are accustomed to sing an octave 
lower than the air is usually played. 

A violin tuner, consisting of four 
small reeds tuned to G, D, A, E, is 
a convenient reference standard to use 
for estimating frequencies. The fre- 
quencies of the four tones are 194, 
290, 435 and 652 respectively. With 
an error of only about three per cent 
these may be assumed to be 200, 300, 
450 and 650, which are sufficiently 
good approximations for our purpose. 

Having one's standard of fre- 
quency, all that remains is to learn to 
recognize musical intervals and to 
know the corresponding frequency ra- 
tios. This is easily done because the 
frequencies which, sounded together, 
are the most pleasing bear the sim- 

Projection Engineering, March, 1930 

Page 15 

Table of Equally 

Tempered Scale, Aa = 










c .... 









c* ... 


















D# ... 



























F* ... 









G .... 









G# ... 

. 25.66 








A .... 









A# ... 


















C .... 

. 32.33 








Fig. 1. — Tins table is based on the International Standard Pitch, A'= 435 vibra- 
tions per second. This pitch ivas established by law in France in 1859 and 
subsequently was adopted to a large extent throughout the musical ivorld. At 
present the tendency is toward Concert Pitch which is about a fifth of a semi- 
tone above International Standard. In the interval from the year 1500 up to 
the present, A' has had values of frequency ranging from 506 vibrations per 
second to 393 — a range of nearly half an octave. A pitch based on C'= 256, 
sometimes known as Philosophical Pitch, is convenient to use in physics because 
the frequencies of all the C's are powers of 2. It is not, however, in general 

use by musicians. 

plest frequency ratios to each other. 
This is characteristic of pairs of tones. 
in both the major and minor scales. 
These scales were developed because 
they were capable of pleasing musical 
combinations ; the simple relation be- 
tween the frequencies was discovered 
long after the scales were invented. 
Bach's invention of the equally tem- 
pered scale did not change this situa- 
tion. Although in the equally tem- 
pered scale the intervals correspond- 
ing to the simple frequency ratios are 
not perfect, they are sufficiently good 
approximations to satisfy most ears. 
In the equally tempered scale the 
maximum deviation from a perfect 
interval is less than one per cent or 
a fifth of a semi-tone. 

In referring to intervals it is best 
to retain the usual musical notation. 
The notes, or degrees, of the scale are 
known as the "first," "second," etc., to 
the "eighth" in rising pitch. The mu- 
sical interval between the first degree 
of the scale and any other is called by 
the name of the higher degree. Thus 
the interval between the first and 
fourth degree of the scale is known as 
a "fourth." The intervals thus defined 
which are the most easily recognized 
are listed in the following table with 
the corresponding frequency ratios : 

Interval Ratio 

Eighth (octave) • 2:1 

Fifth 3 :2 

Fourth 4:3 

Third (major) 5:4 

Third ( minor ) 6:5 

Intervals a whole tone or a semi- 
tone apart may also be estimated 
quite accurately. The frequency ratios 
corresponding to these are as follows: 


Interval Ratio 

Whole tone (large) 9 :8 

Whole tone (small) 10:9 

Semi-tone 16 :15 

The frequency ratios between the 

successive notes of the major diatonic 

scale occur as follows : 

Degree 123 4 5678 
Ratio 9/8 10/9 16/15 9/8 10/9 9/8 16/15 

The ratios given in the first table 

may be checked by taking the product 

of all the ratios between the separate 

degrees of the scale from the first up to 
the degree in question. For example 
the product 9/8 x 10/9 x 16/15 x 9/8= 
3/2, is the ratio corresponding to the 
interval, a "fifth." A minor third is 
the interval between the first and 
third degrees of the minor scale or 
between the sixth and eighth degrees 
of the major scale. 

It is thus a simple matter to com- 
pare the frequency of any tone with 
another of which the frequency is 
known, when the musical interval is 
recognized. For example, suppose the 
standard at hand is 500 cycles, and 
we listen to a tone which is, as nearly 
as we can judge, half way between the 
intervals called a fourth and fifth 
above it. This means its frequency 
is roughly half way between 4/3 of 
500 and 3/2 of 500 which is about 
708 cycles. In such a simple case the 
error could hardly exceed 5 per cent, 
which is 35 cycles. 

If the unknown frequency is more 
than an octave away from the stand- 
ard the only additional step required 
is to pick the nearest tone to one fre- 
quency which is an even octave from 
the other. Remembering that for each 
octave removed we must use a multi- 
plying factor of two (if above) or a 
one-half (if below), the process is the 
same as before. 

As an example of this, suppose the 
unknown frequency is found to be two 
whole octaves and a major third be- 
low the standard, assumed to be 500 
cycles. A tone two octaves below 500 
cycles has a frequency of 500 x 1/2 x 
1/2 = 125 cycles. A major third be- 
low that corresponds 4/5 of 125 that 
is, a frequency of 100 cycles. This is 
then our estimate of the unknown 

A tone an octave above 500 cycles 




Fig. 2. Lissa- 
j o u s figures 
c o rresponding 
to frequency 
ratios for five 
different phase 




Page 16 

has a frequency of 1,000 cycles, which 
is the most popular standard of fre- 
quency used in the laboratory. It is 
evident then that a 1,000 cycle tone is 
just three octaves and a major third 
above 100 cycles. This is true of any 
two tones having frequencies in the 
ratio of 10 to 1. 

A knowledge of the simple fre- 
quency relations corresponding to mu- 
sical intervals is of value when mak- 
ing frequency comparisons by means 
of the Braun tube. It is common 
knowledge that simple Lissajous fig- 
ures are produced when frequencies 
related by a simple fraction are com- 
pared on the Braun tube. The fact 
that the intervals between frequencies 
which form simple Braun tube figures 
can easily be recognized by ear is of 
considerable value in making such 
measurements. In Fig. 2 the Lis- 
sajous figures are shown correspond- 
ing to the simpler frequency ratios for 
five different phase angles, referred to 
the higher frequency in each case. If 
the ratio of the frequencies is not ex- 
actly the value of the fraction indi- 
cated, the figure will change slowly 
through all of the configurations 
shown. Each of the figures shown 
corresponds to a definite and easily 
recognized musical interval. In Fig. 
2 the musical intervals are indicated 
beside the corresponding Lissajous 

The relations just pointed out are 
of value both in estimating unknown 
frequencies and in making actual cali- 
brations. If for example a fairly open 
stationary figure is observed on the 
Braun tube, and the musical interval 
is recognized as a major third, the 
exact ratio of the frequencies will be 
found to be 5 :4. It may in some cases 
be difficult to recognize the difference 
between 5 :4 and 6 :5 Lissajous figures, 
but if the frequencies being compared 
are in the audible range they can be 
positively identified by ear. If it is 
desired to adjust a variable frequency 
to, say, 400 cycles in terms of a fixed 
frequency of 300 cycles, it will be 
found convenient first to adjust the 
variable frequency by ear to a "fourth" 
above the fixed frequency, after which 
only a very slight adjustment will be 
required. The adjustment made by 
ear should be so close that the desired 

Projection Engineering, March, 1930 



Sleep my child and peace at-tend thee 



■3 - U J P 



Three blind mice, three blind mice 


U^l J J-J>rl^ 

There are smiles that make you happy 


5 r J B 

FOURTH-4! 3 


Hal .--le--|u-- J ah l 

HCpTr r r I r 


where and where 

O l J. J *< ii " 



say can you see 





Gone are the days when my 



jjjj i j 



There's mu-'.v in the 

e j I r-*p r- rirre 




Gen— e-vieve. sweet Gen-e-vieve 




OCTAVE - 2:i 

a m 
Last night the night-in- gale woke me 



Way down up-onthe Swanee rlv-er 

Fig. 3. Visualizing musical intervals by means of simple melodies. 

Braun tube figure will be obtained, al- 
though it may be moving rapidly. The 
final adjustment is made by changing 
the variable frequency until the fig- 
ure remains stationary. 

A convenient way to visualize mu- 
sical intervals in question is to note 
simple melodies in which they occur. 
In Fig. 3, a number of familiar 
melodies are indicated which illus- 

trate the intervals mentioned above, 
giving the names of the intervals and 
the corresponding frequency ratios. 
Intervals of the sixth and seventh are 
also given. These are easily recog- 
nized although the frequency ratios 
are not so simple as the others. In- 
tervals visualized in this way are in- 
stantly available for comparing by ear 
any two tones in the audible range. 


DURING the past few weeks the 
public has been taken into the 
confidence of the radio industry 
and shown the true status of 
radiovision, or radio television. In 
Newark, N. J., so-called radio talkies, 
or synchronized sight and sound broad- 
casting, have been demonstrated to the 
radio trade and public. 

Needless to say, radiovision is still 
quite crude. With the limitations of 

the 48-line screen, according to J. E. 
Smith, President of the National Radio 
Institute, Washington, D. C, we can- 
not hope for crisp, sparkling, detailed 
pictures such as we can enjoy even 
with the smallest of home movie out- 
fits. Nevertheless, it is possible to 
represent fair silhouette or shadow- 
graph figures, together with sound 
accompaniment. What is mainly 
needed today to popularize radiovision 
is the radiovision artist, or one who, 
with a technical understanding on the 
one hand, and with true stagecraft on 

the other, can prepare and direct play- 
lets which will really tell a convincing 

Just as in the days of Shakespeare 
the splendid dramas and comedies were 
written and directed for presentation 
with the crudest of stage settings, yet 
survived even to this day because of 
their inherent brilliancy of theme, so 
the radiovision dramas that may be 
written to fit the limitations of our 
radiovision technique, may make a 
name for the true artist. 

Projection Engineering, March, 1930 

Page 17 

Public -Address and Centralized Radio 


IV. Testing Equipment for Disc Reproducers 
By E. W. UArcy 

POSSIBLY a description of a 
type of test equipment designed 
to obtain accurate comparisons 
of reproducers would be of some 
interest to the reader. We will there- 
fore devote a small amount of space to 
the discussion of reproducer testing 

The use of frequency records for 
making tests of reproducer efficiencies 
has the great advantage of economy. 
However, there are many types of re- 
producer actuating mechanisms of un- 
deniable superiority over the recorded 
frequency method. 

It is extremely difficult to reproduce 
a given amplitude repeatedly by means 
of a recorded disc, as there is no way 
to compensate in calculations for the 
wear of a record, or if the pressing 
is not quite up to standard a marked 
discrepancy exists between different 
records of the same frequency bands. 
These disadvantages can be overcome 
by other types of reproducer actuat- 
ing mechanisms. 

The driving mechanism displayed in 
Fig. 25 (see February issue) possesses 
a considerable number of points of 
superiority over the recorded disc 
method of actuating reproducers for 
test. It allows measurements of needle 
displacement to be made accurately, 
at the same time allowing linearity 
response curves, as well as frequency 
response curves, to be made of the 
reproducer under test. In addition to 
this, no element of wear exists, and a 
frequency can be reproduced repeatedly 
with assurance of the same actuation 
of the reproducer armature. 

Mechanical Construction 

The construction of this driving 
mechanism is of extreme simplicity, 
being based on two dynamic driving 
units in order to enable successful 
operation of the mass of the cross 
member and damping device. In prac- 
tice it is impractical to operate the 
complete device from one source of 
applied power, due to the inertial im- 
pedance of the moving members. 
Damping is applied to the system 
through the immersion of the spiders 
and driving coils in low viscosity oil. 

The cross member joining the two 
units is made of hard rubber, and its 
mass weight is kept as low as prac- 
ticable. A slot is filed in the center 
of this cross member, of the approxi- 
mate dimension of the record groove, 
approximately .004 inch deep and .01 
inch wide. Attached at right angles 
to the face of the slot side of the cross 
member is a small concave mirror, 

which deflects the light beam, thus 
allowing magnification of the cross 
member movement on a calibrated 
scale located at a previously deter- 
mined distance from the concave 

The light source and condensing lens 
are normal and can be obtained quite 
easily. No special mention need be 
made of them other than sufficient 
light is required to project the reflected 
light beam a considerable distance, 
and the more powerful the light source 
the more clearly defined the reflected 
light beam will be. 

Uses of This Device. Efficiency of 

This system allows the measurement 
of actuation of the reproducer head to 
be made in an accurate manner. Its 
use, therefore, is practical to measure 
the relation of output energy in mi- 
crowatts as compared to the input 
energy of the same character required 
to produce a measured movement of 
the needle point. 

The following operations are used in 
making these measurements. The dy- 
namic driving units are first oper- 
ated without the additional load of 
the reproducer, and the amount of 
power required to move the cross mem- 
ber a previously determined distance 

The reproducer with its electrical 
load is then placed in position on the 
cross member and the required amount 
of increased excitation to actuate the 
crossarm and reproducer the previ- 
ously determined distance is measured. 

The difference between the no-load 
power absorbed in the driving mechan- 
ism and the power consumed when 
operated with the reproducer load 
added, is then assumed as the power 
required to actuate the reproducer 
head a known amplitude of needle and 
armature movement. 

This power input is then divided 
into the power output of the repro- 
ducer, furnishing an exact measure of 
the reproducer efficiency under the pre- 
viously stated conditions of frequency 
and needle amplitude excitation. 

Linearity Response Curves 

The question of linearity of the re- 
sponse of a reproducer is of consider- 
able consequence in the study of disc 
reproducers, and the use of a driving 
mechanism of the type herein de- 
scribed greatly facilitates the study of 
this effect. 

As stated in the previous article on 
reproducers, the formulae for this 
effect is given as follows : 

V 1 E 1 

V 2 E 2 

V 1 = reference level actuation. 

V 2 = comparative level actuation. 

E 1 = reference level output of re- 

E 2 = comparative level output of re- 

A simple mathematical treatment of 
the system used in making these 
measurements would expedite and fa- 
cilitate their explanation ; so formulae 
are here given — 




250.000 OHMS 




N°. 1 

500 OHMS 

//,/ BOX //A,,/,, 


FIG. 26 


Illustrating function of key switch in relation to resistance network. 

Page 18 

Projection Engineering, March, 1930 

V A = Unloaded dynamic driving 
power for reference level. 

V B = Loaded dynamic driving power 
for reference level. 

E J = Reproducer output at reference 

V c = Unloaded dynamic driving 
power for comparative level. 

V D = Load dynamic driving power 
for comparative level. 

E 2 = Reproducer output at compara- 
tive level. 

V 1 = Reference level actuation. 

V 2 = Comparative level actuation. 

V 1 

V a 
yB v A 

E 1 



E 2 

Any discrepancy on the part of the 
driving mechanism can easily be shown 
and allowance made in the observed 
data for any such discrepancy by the 
means of calibration of the mechanism 
without the load furnished by the re- 
producer under test. This is very 
easily done, due to the facility with 
which measurements 1 of the cross mem- 
ber and consequent driving mechanism 
output power can be made. 

Frequency Response Measurements 

The system just described is very 
accurate and allows exact determina- 
tion of the frequency response of a 
reproducer to be made, due to the abil- 
ity of the mechanism permitting exact 
knowledge of reproducer actuating 
movement at all frequencies. 

Test Set-up for Frequency Re- 
sponse Measurements 

In Fig. 26 a circuit is shown, con- 
sisting of the following component 
parts, each of which will be taken up 
in its order. 


One of the primary requirements of 
measurement of reproducer response is 
that it be tested under loaded condi- 
tions. The author well realizes the 
difference between an inductive load 
and a resistive one. But since a stand- 
ard method of procedure is required 
in making comparative tests of repro- 
ducers and a resistive load is much 
more flexible in respect to impedance 
adjusting than an inductive load, the 
resistive method was decided upon. 

A resistance of 500 ohms is used for 
the terminating impedance of both the 
transducer and standard level. This 
value is merely an arbitrary one, as 
there is no accepted standard at this 

Key switch No. 2 (Fig. 26) is used 
for two purposes. The resistive net- 
work it controls allows an increased 
attenuation of 6 dbs. by means of di- 
viding the input voltage, while the in- 
put impedance, so far as the resistive 
network is concerned, is kept constant. 
Additional variation in input voltage 
is obtained by the 250,000 ohm poten- 
tiometer which is adjustable in 20, 
2-db. steps. 

Use is also made of this network for 
obtaining the impedance of a repro- 
ducer. The diagram is displayed in 
Fig. 27. The theory on which this 
system of measurement is based is 
only accurate where the generator may 
be assumed as being a constant source 
of e.m.f. acting through its a-c. re- 
sistance. These measurements of the 
impedance of a reproducer, therefore, 
are not to be construed as replacing the 
more accurate method of measuring 
the inductance and resistance, then 
calculating the impedance. However, 
the system does allow a reasonable 
accuracy of measurement, and the au- 
thor has found that it is a quite satis- 
factory one, due to the speed with 
which measurements can be made. 

The operations of making these 
measurements are simple and are given 
as follows : The generator whose im- 
pedance is to be measured is con- 
nected to the amplifier input. The key 
is thrown so as to divide the voltage 
appearing across its output. The po- 
tentiometer is then adjusted, so as to 
obtain a convenient setting on the 
amplifier thermo-galvanometer. This 
setting is then noted. The key switch 
is then thrown so the full output volt- 
age is impressed across the 250,000 
ohm potentiometer, and enough resist- 
ance shorted across the generator by 
means of the decade resistance box to 
reduce the output voltage to the level 
previously noted. The resistance of 
the decade box, in use as a short cir- 
cuit, is then assumed as the impedance 
of the generator under test. 

The amplifier used as a level indi- 
cator is a direct coupled type and pos- 






250.000 — 




FIG. 27 

Circuit set- 
ting for ob- 
taining impe- 
dance of re- 


sesses an unusually flat frequency re- 
sponse curve, of the nature of -\ 1, 

db. from 30 cycles to 15,000 cycles. A 
more detailed discussion of this par- 
ticular amplifier will be taken up in a 
subsequent issue. 

The thermocouple galvanometer is 
of an ordinary type. Little need be 
said about the circuit used for bal- 
ancing out the direct current flowing 
through it, as the circuit diagram 
makes this system quite obvious. 

The attenuation box and source of 
the reference level is of some conse- 
quence in this discussion; so we shall 
deal with it in some detail. 

Due to the flat frequency response 
of the level indicator, commercial cur- 
rent is satisfactory to supply the ref- 
erence level. The only requirement is 
that the impedance of the source of 
supply must be 500 ohms at all frequen- 
cies. Means for regulating the current 
flowing in this circuit without affect- 
ing the impedance also should be in- 
corporated. "O" level for these meas- 
urements is assumed to be a current 
of 4.475 milliamperes flowing through 
a load of 500 ohms. 

The attenuation box is designed to 
operate between a source and load, 
both of which must possess an im- 
pedance of 500 ohms. 

The operation of this equipment is 
very simple. The voltage appearing 
across the 500 ohm load resistor is 
first measured with the reproducer 
operating through the transducer con- 
nected by means of key switch No. 2. 
The key switch is then thrown so as to 
connect the level standard to the 500 
ohm load, and enough attenuation is 
introduced by the attenuation box to 
duplicate the voltage appearing across 
the 500 ohm load resistor, generated 
by the reproducer. The gain of the 
reproducer can quite easily be calcu- 
lated then, as the loss through the 
transducer can be considered a positive 
one and the loss through the level 
standard a negative one. Adding 
these two values algebraically gives 
the gain of the reproducer in decibels. 
(To be continued) 


ONE of the most beautiful the- 
atres in the United States, the 
New Casino on Santa Catalina 
Island, California, will open 
soon with RCA Photophone sound re- 
producing equipment. Avalon, the 
small resort city which nestles in a 
bay below the hills of the island, at- 
tracts thousands of visitors and is one 
of the sights of interest to the majority 
of tourists who make the rounds. The 
theatre occupies the greater part of a 
small peninsula that juts out into the 
Pacific and is said to be one of the 
finest in all America. 

Projection Engineering, March, 1930 

Page 19 

Effect Lighting in Theatres 

Original Account of Present-day Methods of Producing Various Realistic 

Effects on Theatre Screens. 

James R. Cameron 

today, especially as found in 
many of the de luxe houses, 
represent a combination of 
the earlier "straight movie" shows 
with a trimming of vaudeville num- 
bers formed against a musical back- 
ground provided by an organ, orches- 
tra, or stage band. 

There are exceptions to this formula, 
of course, but animated performers, 
assisted by music provided by one or 
more means, are used to supplement 
the motion pictures which still con- 
stitute the principal body of the pro- 

With the fusion of these two, 
hitherto widely separated types of 
entertainment, it was only natural that 
the theatrical atmosphere which 
formed a part of the legitimate stage 
setting should also be used in con- 
structing the modern form of enter- 
tainment peculiar to the presentation 
of motion pictures. 

This rather indefinite, almost intan- 
gible, "something," usually referred to 
as "atmosphere," is provided for the 
large part, by means of effect lighting. 
In its general aspect, so-called effect 
lighting is composed of three very 
broad divisions, as follow : 

1. The projection of animated 

scenic effects. 

2. The projection of color effects. 

3. The projection of simple masks, 

cut-outs and special lantern 

The last two of the above named 
divisions are of comparatively recent 
origin, at least as regards the par- 
ticular manner in which they are ap- 
plied to the presentation of motion 

Animated scenic effects, however, 
were used on the legitimate stage a 
score or more years ago and they have 
been retained, with practically no 
changes, until the present time. 

Animated Scenic Effects 

In general, scenic effects are 
imaged upon a suitable curtain, drop, 
or scrim by the simple expedient of 
placing a revolving transparent disc, 
on which the particular effect is 
painted, or photographed, before a 
projection lens, much in the same 
fashion that a slide is projected by a 
stereoptican lantern. Indeed, many of 
the commonly used effects are nothing 
more than special, elaborate, lantern 
slides so designed as to repeat them- 
selves continuously tipon the screen. 
The driving power for these effects 
may be obtained from either a double- 

spring clock-work motor or an electric 
motor, attached to the metal casing 
which encloses the revolving disc for 
purposes of projection and attachment 
to the projector. 

Mica is used in constructing the discs 
because it has the advantages of light 
weight ; does not readily break ; is 
suitably transparent ; and above all, 
withstands a high degree of heat. 

In the case of certain scenic effects, 
such as clouds and panoramic views of 
floods and cyclones, which are focussed 
in a fairly sharp manner upon the 
screen, the parts of the effect consist 
of simply the effect disc, the protective 
casing and the actuating, adjustable 
speed, clock-work motor. 

Other effects, such as flames, ocean 
waves, babbling brook, etc., use the 


Never in the history of any other 
industry has such an array of 
money making opportunities been 
presented as are outlined in a 
comprehensive article to appear 
in the April issue of Projection 
Engineering. This story was 
written by N. M. Simons and it 
has to do with the uses of and 
markets for Sound Amplifiers. 

same parts in their construction with 
the addition of a 5-inch diameter glass 
ripple plate inserted just in front of 
the projected portion of the disc, so 
that the projection lens, sees the disc 
through the rippled glass. The plate 
serves to give an irregular fused- 
motion effect to the local areas on the 
disc which would otherwise move 
across the screen in sharply defined 
rigid fashion. Some effects, as for in- 
stance, rain and snow, make use of 
either a special disc, or a special plate 
placed before the disc in such a posi- 
tion that both elements are projected 
at the same time. 

In the case of rain the standard 18- 
inch mica disc is used, the entire disc 
being opaque with the exception of 
the rain drops which are represented 
by elongated clear portions of mica for 
passing the light. 

A rain plate, consisting of two sepa- 
rate plates of either glass or mica, on 
which have been printed closely spaced 
opaque lines, the plates then being 
placed together and rotated at a slight 
angle to form a zig-zag pattern, is then 
placed in front of the rain disc to 

break up the drops and give the effect 
of a shower. 

A special disc is used in the case of 
snow, this being of a firm, opaque 
material in which have been punched 
many small holes (representing the 
snow flakes) closely spaced to simulate 
either a heavy or light snowfall, as 

Each effect disc is provided with a 
holding plate, the edges of which are 
turned over to form a lip so that the 
effect casing can be slid into a suitable 
holding plate on the projector in the 
same fashion that a colored gelatine 
is placed in position in front of a 

These holding plates on the effect 
casing are not rigidly fastened but can 
be swiveled completely around to per- 
mit of the effect casing being rotated 
when in position before the projector 
condenser lenses. In this manner the 
effect, as shown upon the screen, can 
be made to sweep across it in any de- 
sired direction. 

Some effects require two elements, 
one of which consists of a suitable 
lantern slide or a metal stencil-mask 
placed in the slide carrier of the pro- 
jector. Of such a type is the waving 
flag effect wherein a lantern slide of 
a flag is projected to the screen 
through the slots of a spoked wheel 
which revolves at a point between the 
projection lens and slide. The wave 
motion is imparted to the flag by the 
shadows of the wheel spokes sweeping 
across the projected image on the 

Rainbow and Lightning Effects 

Other examples of two-element ef- 
fects are the rainbow, aurora-borealis 
and lightning effects. The first named 
uses a stencil of a rainbow cut in a 
metal mask which is then placed in 
the slide-carrier for imaging on the 
screen, and in front of the projection 
lens is placed a prism box containing 
two optical prisms for imparting the 
necessary rainbow colors to the image 
on the screen. 

Some effects are quite complicated 
as to structure, a good illustration 
being the moonlight water ripple (a 
two-element effect using a ripple-box 
and a metal mask). Three ripple 
plates are used in this device, each 
plate consisting of an opaque field 
across which fine water ripple lines 
weave so as to overlap and form a 

These three plates are then caused 

Page 20 

Projection Engineering, March, 1930 

to move up and clown by means of a 
clock-work motor, being thrown out of 
step (120°) with each other by means 
of three eccentric hubs on the motor 
shaft ; each ripple plate being joined 
to its respective hub through a driving 

There are any number of animated 
scenic effects which can be devised, 
but in general, all of them are oper- 
ated in one of the ways described 

Scenic lantern slides, in combination 
with an effect for imparting motion 
to certain areas contained in the 
picture, are also commonly used. Thus, 
in a slide of a camp-fire group, a flame 
effect can be used to show a realistic 
camp-fire with the flames leaping from 
the logs ; or a mountain waterfall can 
be shown with the water tumbling 
over the brink of the fall to the bot- 
tom ; or still further, the water in the 
pool at the base of the fall can be 
made to swirl about. 

Indeed, by means of animated effects, 
volcanoes can be set into action ; the 
fury of the elements invoked ; and 
scenes can skip quickly from arctic to 
tropics, from summer to winter — while 
the patrons sit high and dry, in com- 
fortable seats, with their goloshes and 
umbrellas safely parked in the vesti- 
bule at home. 

Color Effects 

Color effects, as projected from a 
special "spot booth" or from the pro- 
jection room proper, are used in pro- 
logue work, special numbers, organ 
solos and even in the showing of 
motion pictures. 

The principal control, in the case of 
simple colored lighting effects, consists 
in changing the colors themselves, or 
in changing the shape of the projected 
floods or spots. 

Thus, a round, square, rectangular, 
or any odd-shaped colored spot or flood 
may be projected singly or in combina- 
tion with one or more spot or floods 
of special shape to obtain a blending 
or dissolving color action on the stage. 

When the standard, double-optic 
system type of effect projector is used, 
two different colored beams, of any 
desired shape, as for instance, square, 
may be dissolved back and forth to 
obtain other than those represented 
by the gelatines used in the projectors. 
Or a square flood may be placed around 
the organ and the organist "head- 
spotted" with either a clear or colored 
round "spot." Combinations in this 
respect are quite numerous. 

A very pretty effect, and one which 
is often used in title and border work 
while motion pictures are being shown, 
is found in the use of special glass 
design plates which are sharply imaged 
on the screen (or around the picture 
area) after which a special color wheel, 
consisting of narrow widths of various 
colored gelatines, is placed in front of 
the projection lens so that the colors, 
as they pass before the lens, are caused 
to weave across the imaged design on 

the screen, a peculiar blending and 
fading in-and-out effect being obtained. 

As used in connection with film title 
work, this color effect serves as a pre- 
lude to the principal title and is oper- 
ated in the following manner. A blank 
leader, of a length consistent with the 
period of time it is desired to show the 
colored effect, is spliced between the 
last reel of one subject and the first 
reel of the next succeeding subject so 
as to make a complete 2000 ft. reel. 

The projectionist, taking a cue from 
the end of the last reel as it passes 
through the projector, is stationed at 
the effect projector and when the cue is 
received he gradually opens a pair of 
vertical framing shutters which causes 
the blending color effect to be seen on 
the otherwise dark screen as if appear- 
ing from behind a pair of slowly open- 
ing draw curtains. 

This effect is allowed to stand on 
the picture screen while the blank 
leader is being run through the pro- 
jector and even after the title is pro- 
jected onto the screen, the colored 
effect then serving as an animated 
field. Just before the picture comes on, 
the projectionist slowly closes the 
framing shutters, thus making the 
effect apparently disappear behind the 
closing curtains, leaving the motion 
pictures to follow closely on its heels. 

By means of a special mask, pro- 
vided for the purpose, the same effect 
can be projected around the border of 
the motion picture and left there until 
that particular subject is finished ; or 
else a new design may be dissolved 
upon it to take its place, thus con- 
stantly changing the effect obtained. 

Masks, Cut-outs, and Special Slides 

By far the greatest number of orig- 
inal effects are obtained by the use of 
simple masks, stencils and, in special 
instances, lantern slides. It is here 
that the ingenuity of the projectionist 
finds its greatest field and many, in- 
deed, have become quite proficient in 
this work. 

Stencils of flowers, ships, hearts, 
vases, crosses, and many other objects 
are legitimate prey for such effects and 
are eagerly seized upon by projection- 
ists in their quest for the novel and 
original. One man in St. Louis has 
made a stencil of every conceivable 
kind of flower, including a few that 
possibly never grew ; another in Engle- 
wood, N. J., has a penchant for ships 
and on the slightest provocation will 
project a figure of a vessel of some 
kind upon the titles of all marine films. 

This work is unique and never be- 
comes tiresome except for the physical 
exertion required, since an illustrative 
point in the current feature picture can 
be made to serve as the subject. 

Feature pictures, prologues, skits and 
special acts may serve as the inspira- 
tion for projecting novel and original 

To Spotlamp Effect Projector 

In its simplest form, an effect pro- 
jector is nothing more than a spotlamp 
to which have been added an extra con- 

densing lens for converging the light to 
make it pass through an effect (at- 
tached to lens holder plate) and then 
on to a projection lens (attached, in 
turn, to the effect casing). 

This simple device was designed pri- 
marily for use "back-stage" where it is 
particularly effective in that it can 
readily cover a large area on a short 
projection distance ; can be stripped of 
its accessories and impressed into spot- 
lamp duty when required. 

Its adaptability to short focal length 
lenses for covering large areas at lim- 
ited distances really acts as a powerful 
deterrent to its use in the projection 
room where, because of the greatly in- 
creased projection distance, long focal 
length lenses are required. There are 
no or-dinary means for rigidly support- 
ing such lenses on this unit and, 
indeed, even if there were, the device 
would be quite cumbersome and diffi- 
cult to handle with ease and rapidity. 

Furthermore, it can project only 
single effects so that the use of double 
effects would require two such units 
and two operators. 

Modern practice in motion-picture 
theatres only served to accentuate the 
inconveniences of such limitations and 
it was early realized that for this ser- 
vice a special unit, particularly designed 
to meet the conditions in picture thea- 
tres was essential for proper effect 

It is true that efforts were made, 
and for that matter still are being 
made, to apply the spotlamp effect pro- 
jector to projection room operation, 
but a single demonstration, wherein 
rain drops appear of balloon propor- 
tions and snow flakes take on the ap- 
pearance of a bombardment by snow- 
balls, serves to convince the economical 
aspirant of the futility of his efforts. 

The spotlamp type of effect projector, 
therefore, is definitely limited to back- 
stage service. 


RECORDED programs have been 
argued pro and con by the radio 
stations, advertisers, and public 
alike. Would such programs 
cut into the profitable network broad- 
casting? Might it be used for supple- 
mentary broadcasting? Could inde- 
pendent stations better their reputa- 
tions by using recorded sustaining pro- 
grams? Would the public accept them? 
Should not the expensive programs of 
quality, prepared by the leading 
sponsors, be recorded in permanent 
form for supplementary and repeat 

The upshot of the matter is that 
recorded programs are being recognized 
as one of the greatest forces for more 
and better presentations by the leading 
sponsors. It is the boon of the small 
station as well as the large. 

Projection Engineering, March, 1930 

Page 21 

Mobile Recording 1 

The Recording Technique of Dramatic Productions on Location 

By Carl Dreher* 

MOBILE recording in sound 
motion-picture work includes 
newsreel applications and "lo- 
cation" jobs, which applies to 
any part of a production not made in 
the studio. The location may be on the 
grounds of a Beverly Hills estate, at 
the seashore, in the desert, or in any 
other place appropriate to the action 
of the photoplay. This article is con- 
cerned principally with the recording 
technique of dramatic productions on 

In many ways out-of-the-studio re- 
cording taxes the ingenuity of the 
sound technician to a greater extent 
than stage work, just as the broad- 
caster meets problems in field work 
that are not encountered in his own 
building. The hazards of temporary 
connections, damage to equipment in 
transit, extraneous noise, and the lim- 
itations of transportable equipment, 
must all be faced. On the other hand, 
acoustic conditions, barring noise in- 
terference, may be as good or better. 

Principal Elements 

In the studio the connections be- 
tween the units are likely to be largely 
in the form of standard electrical wir- 
ing in conduit. On location a good 
part of the connections is likely to run 
through temporary cables laid on the 
ground. In the studio the recorder 
may operate off the city power supply : 
on location a generator driven by a 
prime mover is likely to be the source 
of power. 

A single closed motor-truck is gen- 
erally vised for the transportation of 
the equipment. Usually two motor- 
trucks are utilized, one for supplying 
power, the other for amplification and 
recording. In newsreel work all the 
equipment is in one truck, but the prin- 
ciples of operation are the same in the 
two cases. 

While standardization in this field 
is far from complete and there are 
wide variations in the equipment con- 
sidered necessary for location record- 
ing by the various producers, the fol- 
lowing list of master items covers the 
average outfit : 

(1) Motor-truck, l%-2 ton size. 

(2) Microphones, generally of the 
condenser type with associated ampli- 
fiers (three to twelve). 

(3) Recording amplifier (one or 
two) with associated control and meas- 
uring equipment. 

(4) Film recorder (one or two). 

(5) Camera equipment, including 
means for synchronous driving. 

(6) Film magazines and accessories. 

(7) Intercommunicating telephones. 

(8) Connecting cables. 

(9) Power supply (inverted rotary 
• •(inverter or motor generator ; storage 
batteries: dry batteries), and control 

Mobile recording may be done on 
wax, but this is in the nature of a 
special development and the descrip- 
tion here will be confined to recording 
on film. 

Service Requirements 

The service requirements of each of 
the main elements of a mobile record- 
ing system, as enumerated, will be dis- 
cussed briefly. The truck, first, must 
be large enough to hold the apparatus 
and three or four operators. The 1%- 
ton size shown in Fig. 1 is adequate 
for most purposes, but a 2-ton machine 
affords more room and is usually pref- 
erable. Speed, ability to traverse all 
kinds of country, and easy riding qual- 
ities are all essential. Speed is always 
necessary in the movies, because of the 
inordinate expense of production — 
quite an ordinary picture may run to 
$10,000 a day on location. Ability to 
get anywhere is equally essential, since 
locations are not picked for accessibil- 
ity alone ; the truck may have to go 
up mountains or into desert country 
where the roads are merely paths in 
the sand. It is expected to reach any 
place where a passenger car with a 
powerful motor and good chassis con- 
struction can penetrate. And the truck 
must ride easily, for the protection of 
its load of delicate equipment in tran- 
sit. When it gets to the location the 
lenses, tubes, and connections must be 

intact, to mention only a few of the 

The microphones supplied with a mo- 
bile recording channel generally do 
not differ from the condenser trans- 
mitters with associated amplifier en- 
cased in the same shell, which have 
become standard in sound picture work 
because of their low background noise, 
ability to work in any position, and 
mobility during a take. The record- 
ing amplifier and the recorder proper 
are also likely to be the same as in 
the studio. Only a few models of film 
recorders have been developed, and 
most studios have only one type, so 
perforce the same equipment is used in 
fixed and movable installations. There 
is more chance for variety in the am- 
plifiers. While the studio types, suit- 
ably mounted, are often utilized, there 
is a tendency in the field to use tubes 
with low power consumption, and some- 
times it is expedient to split the stages. 
For example, the microphone may 
have two stages in its associated 
amplifier, followed by three stages in a 
portable, dry-battery operated ampli- 
fier of the broadcast type, located 
relatively near the pickup point, this 
in turn feeding an output unit of one 
or two stages in the truck close to the 

Camera Equipment 

Camera equipment for dramatic loca- 
tion work is rarely carried in the sound 
truck. The camera department usually 
has a truck of its own capable of car- 
rying four cameras and the necessary 
tripods, dollies or camera trucks 
(equipment for photographing with the 
camera in motion) and other accesso- 
ries. In newsreel work, however, the 
picture-taking equipment goes with the 
sound truck. In either case the cam- 
eras are driven synchronously with the 

t From the March, 1930, issue of "Radio 


* Director of Sound, R-K-O. 

Fig. 1. R-K-O sound truck. 

Page 22 

Projection Engineering, March, 1930 

Fig. 2. Left to right: mixing panel, 
battery box, amplifier rack 

recorder by electric motors and asso- 
ciated control equipment. Since pic- 
ture and sound are usually photo- 
graphed on separate films and com- 
bined in printing, marking facilities 
must be included. Marking is accom- 
plished electrically by fogging the 
sound track and the edge of the pic- 
ture film ; a simpler expedient is to 
slap a pair of hinged sticks together 
near the microphone and within the 
camera field, resulting in characteris- 
tic marks on the sound track which 
are then matched with the picture 
frame showing the sticks meeting in 
the impact. 

Sound trucks usually carry sis to 
sixteen 1000-foot film magazines for re- 
cording, and of course means are pro- 
vided for renewing the supply of unex- 
posed film constantly. Both the 
sound and camera departments must 
develop test strips of film on the spot, 
to ascertain exposure conditions, posi- 
tion and density of sound track, etc. 
This is accomplished by means of a 
light-tight box large enough to hold 
in the bottom a jar of developer, a jar 
of water, and a jar of fixing solution. 
A film magazine mounts on top over a 
trapdoor which permits access for fill- 
ing the jars. One side of the box is 
black cloth with two sleeves in which 
the operator inserts his arms. An 
elastic band within each sleeve makes 
the joint light-tight. The exposed strip 
is pulled down out of the magazine, 
passed through the developer for an 
appropriate time, washed, immersed in 
the Hypo jar for fixing, washed again, 
and removed for drying and inspection. 
For developing very small quantities 
of film where the photo-chemical ele- 
ments are not critical, such a box is 
the equivalent of a dark room. 

Not much need be said about inter- 
communicating telephones, which in 
general do not differ from the headsets 
and breast transmitters familiar in 
broadcast or picture studio practice. 
Cables and plugs, however, are of the 

utmost importance. The massive type 
of termination employed for micro- 
phone cables is shown on the left side 
of Fig. 2. The currents passing 
through such a connection are insig- 
nificant and would normally require 
only the lightest kind of plug-and-soc- 
ket combination, but in a business 
where noise-free, perfectly tight, water- 
proof connections are vital, it pays to 
use only heavy contact equipment. The 
insertion having been made, the connec- 
tion is locked by means of a heavy 
threaded ring. Note also the size of 
the rubber-covered cables and the me- 
chanical reinforcing where the cable 
enters the plug. 

Power Supply 

The principal problem in mobile re- 
cording is the electrical power supply 
for the equipment. This breaks down 
into the following elements. 

(1) Alternating-current supply for 
interlocking cameras and sound re- 

(2) Filament supply for amplifier 
tubes and exposure lamps, marking, 
etc. (Usually 6-12 volt storage bat- 

(3) High voltage for polarizing con- 
denser transmitters and for amplifier 
plate supply. , 

The alternating voltage is usually 
110/220 volts, 3 phase, 50/60 cycle. 
The reason for the alternative fre- 
quencies is that most of the Western 
picture studios are located in a section 
of Los Angeles where the municipal 
power supply is 50 cycles, and they 
usually prefer to use the same cycl- 
age for studio and location work, so 
that all the recorders may be inter- 

Fig. 3. 

Interior of R-K-O sound 

Fig. 4. Interior of Paramount 
sound truck. 

changeable. The a-c. generator is 
often not coupled directly to a prime 
mover, because of the difficulty of 
maintaining the close speed regulation 
necessary. Instead, there may be a 
separate power truck in which a gaso- 
line motor drives a d-c. generator 
which supplies power to a d-c.-a-c. 
motor generator, or inverted rotary 
converter, with appropriate voltage 
regulators, speed regulating, control- 
ling, and metering equipment. The 
trouble' with this combination is that 
noise from the gasoline engine may 
interfere with recording nearby. 
Hence a 32-volt storage battery is fre- 
quently utilized to supply power for 
a d-c.-a-c. motor generator set, the 
motor of which is a 32-volt d-c. ma- 
chine. This arrangement is relatively 
quiet and in the open air may be used 
a few hundred feet or less from the 
pickup point. The storage battery is 
charged during the night or when 
shooting is not in progress by a gaso- 
line-driven charging generator, or, if 
an electric power supply is available, 
through a resistance or rectifiers. In 
newsreel work, for example, the truck 
is generally stored in a garage over- 
night, and both d-c. and a-c. chargers 
are included in the equipment, so that 
it is only necessary to connect a cable 
to the power supply. On location, 
however, the company may be work- 
ing far from any electric power sup- 
ply, and hence the ultimate source of 
power must be a prime mover. This 
may be the automotive engine itself, 
equipped with a power take-off on the 
transmission of the truck. Of course 
charging facilities include provision 
for the storage batteries used to sup- 
ply filament power. 

The power units employed in vehi- 
cular sound-picture recording are quite 
large, because of the need for con- 
stancy under varying conditions. Stor- 
age batteries for filament supply are 

Projection Engineering, March, 1930 

Page 23 

usually of the 100-150 A.H. size. The 
gasoline motor for a large location 
truck's d-c. and a-c. power supply may 
rate 10-20 h.p., the charging generator 
about 1 kw., and the alternator may be 
about 2 kva., even though the total of 
the ratings of the camera and recorder 
motors which it supplies is not over 
0.5 kva. Such motors run about 1/20 
horsepower for a camera motor and 
1/10 horsepower for a recorder motor. 
Plate and condenser transmitter 
polarizing voltages are most con- 
veniently derived from dry batteries, 
although sometimes a small motor 
generator set, properly filtered, is em- 
ployed, and small storage batteries 
with a few ampere-hours capacity are 
also in use. 

Actual Operation 

The actual operation of a sound 
truck on location is like driving an 
automobile in traffic — there are some 
general principles but no two situa- 
tions are alike and one can never 
afford to fall asleep. The principal 
additional problems are noise (includ- 
ing wind) and testing remote from a 
laboratory. As far as noise goes, the 
a-c. power truck itself is a possible 
source, and it must be so placed that it 
does not interfere. Distance, of course, 
is usually the best cure, and it is some- 
times necessary to get as far as 700 
feet away. Usually there are also 
large power trucks for lights which 
may disturb the recording. Some of 
these machines run from high-tension 
lines, the motors being 2200 volts a-c, 
and although they may develop sev- 
eral hundred kilowatts of power, they 
are less likely to interfere with record- 
ing than smaller gasoline operated 
units. But the worst obstacle in out- 
door recording is wind. Various 
microphone shields and protectors 
have been developed, but none are bet- 
ter than palliatives. They reduce the 
wind noise at the expense of high- 
frequency pickup. It depends on the 
nature of the action, the voices of the 
actors, whether the production is on 
schedule or behind, and on other such 
factors, as to whether in the judg- 
ment of the director and the sound 
engineer shooting should continue or 
not. If the pickup is an easy one and 
the job must be completed quickly, it 
may be advisable to shoot sound dur- 
ing a moderate wind. If the situation 
is less urgent, and the time may be 
filled in by silent shots, it may be bet- 
ter to postpone recording until condi- 
tions are more favorable. Incidentally, 
even if the scene requires wind it is 
usually better to shoot under quiet 
conditions and then to dub in wind 
noises artificially in the exact volume 
and tempo required. Actual wind is 
much less obliging in these character- 
istics than a "sound-effects man" turn- 
ing the crank of a wind machine. 

As in studio recording, the camera 
runs synchronously with the recorder 
at 90 feet a minute, corresponding to 
24 pictures a second, and the two ma- 
chines are interlocked by synchronous 

motors or by special circuits of the 
type described by H. M. Stoller in 
"Synchronization and Speed Control of 
Synchronized Sound Pictures," Trams. 
8.M.P.E., Vol. XII, No. 35. The fre- 
quency of the driving source is checked 
by a frequency meter, and it is also 
well to guard against large deviations 
in either recorder or camera speed by 
checking the footage of each take 
against the time, and checking the re- 
corder against the camera on some 
takes. Both instruments are supplied 
with footage counters, so this is not a 
difficult operation. The skillful utiliza- 
tion of such expedient, electrical, op- 
tical and mechanical, is what makes 
a successful location recordist. Of 
course he requires the usual electrical 
and optical testing equipment, such as 
an audio oscillator, meters, a photo- 
meter, etc., but as most of these instru- 
ments are readily portable there is no 
reason why they should not be avail- 
able on location jobs. Finally, spare 
parts, and plenty of them, are needed. 
The greater the distance from the base 
of supplies, the more spare parts 
should be provided. In the case of an 
important picture in a remote location, 
two recording channels are practically 


^/4X y 






- 1 



'40> //// 

Fig. 5. 

Diagram of recording ap- 

essential ; the producer stands to lose 
almost the price of a recording channel 
if he does not recognize this. 


Recording at the studio over wire 
lines from a remote point has been 
successfully attempted, but it is too 
complicated to be practical under 
normal conditions. The time lost in 
communication, the lack of immediate 
contact between all the sound and pic- 
ture technicians involved, and the dif- 
ficulty of maintaining synchronism ex- 
cept where a common power supply 
happens to be available, are adverse 
factors. There may be cases, however, 
where sending sound by wire or radio 
telephone to a producer or supervisor 
at the studio may prove to be a useful 
expedient in production. 

The director, camera man, and sound 
recordist on a production are guided 
largely by the daily "rushes," which 
are returned from the laboratory as 
soon as possible. One of the difficul- 

ties of location work is that the com- 
pany on location must either rely on 
criticism of the rushes by others at the 
studio, or send men in to the studio by 
airplane or automobile to get the re- 
ports. A portable reproducing outfit 
at the location is a highly useful im- 
plement in this connection. 


tion-picture engineer asso- 
ciated with Fox Movietone, 
has witnessed much of change 
and improvement in the talking-picture 
art since, nearly twenty years ago, he 
produced the first Edison "talkies." 

The recent introduction of Grandeur 
film by the Fox Film Corporation 
created quite a sensation in moving- 
picture circles, and the showings also 
immediately caught the fancy of the 
movie patrons, who have been loud in 
their praise of the innovation. 

The first showing of Grandeur was 
given at the Gaiety Theatre, New 
York, in September last. The Roxy 
Theatre, New York, is now equipped 
for the showing of Grandeur. 

Grandeur film is twice the standard 
size ; the ordinary being thirty-five 
millimeters wide, one-tenth of an inch 
off for the sound track. With the film 
becoming smaller (due to the provision 
for sound track), while at the same 
time theatres everywhere are being 
made larger, the use of the former 
regulation size of film has left much 
to be desired in the way of preserving 
familiar proportions. 

Grandeur film restores the natural 
oblong vision effect, and gives the 
performer the needed elbow room. 
Grandeur being twice the width of 
standard permits of groups of perform- 
ers being shown life-size. There is 
also the advantage that one-fourth inch 
may be allowed for the sound track 
in place of the standard one-tenth inch. 
This makes higher quality possible and 
a satisfactory volume of sound may be 
produced with less amplification. 


THE property of a vacuum tube 
to oscillate at audio frequencies 
is used in an "electric organ," 
which was used in a program 
through KDKA recently. The instru- 
ment, invented by R. C. Hitchcock, was 
played by Charles Heinroth. 

It consists, essentially, of a bank of 
tubes which can be caused to oscillate 
at various frequencies, thus producing 
various notes and chords. These oscil- 
lations are fed to the first stage of a 
powerful audio amplifier and repro- 
duced by means of a dynamic speaker 
mounted on a large baffle. 

Page 24 

Projection Engineering, March, 1930 

What the Motion Picture Means 

to the World 

An Address By Will H. Hays, President Motion Picture Producers 
And Distributors Of America 

ONE stands on a high mountain 
and sees long lines of men and 
women and children moving 
slowly forward. They come 
from everywhere. They are rosy 
cheeked girls from the farms and their 
paler faced sisters from the cities 
whose feet ache from long hours of 
standing behind bargain counters. 
There are plow boys and sons of mil- 
lionaires and boys with the sallow 
cheeks of the tenements. There are 
old women with hands reddened and 
coarsened by work and with eyes grown 
listless with long waiting. There are 
old men who hobble on crooked sticks 
and children with the flash of the sun's 
gold in their hair and the happy 
laughter of innocence in their voices. 
There are the schoolboy and the savant 
and man of no learning at all. There 
are men and women of every race and 
of every tongue moving slowly forward 
seeking something — seeking, searching, 
yearning, asking for a place to dream. 
All about them is the roar of the cities, 
the confused jangling noises of life 
that is hurried, rushed, propelled for- 
ward at a breathless speed. Every 
minute of every hour of every day 
they come. Millions of them stop and 
over and above them and in front of 
them attracting them on, offering that 
which they desire, are billions of 
flickering shadows. 

The motion picture, who shall esti- 
mate its importance? Who shall at- 

tempt to say what it means to the 
world? The motion picture within the 
thirty years of its existence has be- 
come a necessity. In thousands of 
homes throughout this country the 
question is not "Shall we go to the 
movies?" It is. "To which movie shall 
we go?" The whole story of the mo- 
tion picture is most fascinating. No 
story ever written for the screen is 
as dramatic as the story of the screen 
itself. In one of our great cities 
recently there was a theatre strike. 
The theatres were closed. For two 
nights a million people milled about 
the streets bereft of entertainment. 
The city authorities sent word that 
the theatres would have to re-open. It 
was necessary for the well-being of 
the city that a place of amusement 
and relaxation be provided for that 
vast citizenry. And so the theatres 
were opened. 

Hollywood where most of the pic- 
tures are made is an international 
enterprise. • Producers, actors, writers 
have their eyes on the world when 
they make pictures. There is an 
earnest effort to consider the national 
feelings of other countries and to 
present the citizens of one country in 
such a sympathetic light that all other 
nations will be friendly with them. 
The producers are eager to aid in the 
world movement for peace. They are 

as eager too, of course, to make pic- 
tures which will please everyone at 
home. Obviously, it is difficult in a 
country where there is wide divergence 
of opinion upon religion, politics, art 
to please everyone with every picture. 
The industry is glad, however, to have 
expressions of opinion from all pos- 
sible sources that it may more nearly 
please everyone and it will con- 
scientiously analyze and, if possible, 
make use of every constructive sug- 
gestion and criticism. 

Since the advent of talking pictures 
and by reason of the industry's own 
care of its standards and quality, in- 
terest in screen entertainment has 
grown enormously. Last year's attend- 
ance increased fifteen million per week 
in this country alone. "Music hath its 
charms," indeed, as producers now 
know. Dialogue has made possible the 
use of a great field of plays and 
books which formerly had no screen 
value. The present is great but the 
future of motion pictures is greater. 
In this hour of salute to motion pic- 
tures, the industry takes the oppor- 
tunity to extend its felicitations to our 
many friends and to the Westinghouse 
Company and to assure you that we 
are seeking to the best of our ability 
to serve the great entertainment loving 
public with pictures of the highest 
quality of artistry and beauty. 


THE Society of Motion Picture 
Engineers will hold its Spring 
convention at the Wardman 
Park Hotel, Washington, D. C, 
May 5-8, according to the announce- 
ment of the Board of Governors. 

The various committees of the society 
are already at work preparing a well- 
rounded program of papers and enter- 
tainment for the convention, and it is 
expected that this convention will be 
the most constructive and valuable yet 
held by the society. 

"While it is quite likely that details 
of sound picture production will receive 
a large share of treatment," reports J. 
W. Coffman, chairman of Papers Com- 
mittee, "the Society recognizes the fact 
that the industry is now well stabilized 
in sound picture production and that 

the sound picture is the standard pic- 
ture today. The sound technician is 
now regarded as an integral part of the 
industry rather than an outsider." 


THE motion picture theatre fire 
in Paisley, Scotland, on the last 
day of 1929, in which seventy- 
two or more lives were lost, 
completes a most tragic record of death 
and destruction chargeable to nitro- 
cellulose film during the year. If we 
may judge from the newspaper reports 
it was simply another case of improper 
arrangements for film projection, in- 
adequate exits, and panic. 

Starting with the Cleveland Clinic 
fire in May, there has been a veritable 
epidemic of serious fires involving 
nitrocellulose film. These fires reflect 

* N.F.P.A. Quarterly. 

no new hazard. They perhaps merely 
represent the operation of the law of 
averages, compensating for a period of 
years when the hazard was ever 
present but during which few serious 
nitrocellulose film fires happened to 

No new lesson is involved. Nitro- 
cellulose film is an extrahazardous 
material. This hazard can be amply 
safeguarded by the application of the 
safety measures long recommended by 
the National Fire Protection Associa- 
tion and all fire prevention authorities. 
A safe substitute, cellulose acetate 
film, is available for use wherever the 
complete safeguarding of the nitrate 
film is not practicable. Is it too much 
to hope that the tragic record of 1929 
will shock the public into a full realiza- 
tion of the hazard of nitrocellulose 
film, with resultant application of the 
necessary fire-safety measures? 

Projection Engineering, March, 1930 

Page 25 

Talkie Dominance a Tribute to Holly- 
wood's Creative Minds 

STARTLING changes are destined 
to come to the screen during the 
next few years — changes which 
will include such revolutionary 
features as super-sized, stereoscopic, 
all-color talking and musical pictures. 

Although the early hectic days of 
talkie-making are over, progress and 
improvement will not cease. Radio 
Pictures' recent acquisition of the 
Spoor-Berggren wide-film process will 
bring to the theatres of the world the 
result of years of laboratory experi- 
ments made at a cost of millions of 
dollars. It will not be long before our 
entire conception of talking-picture 
exhibition will change. The screen will 
have a new and thrilling enlargement. 

Flexibility of thought, the ability of 
the mind to adapt itself to new con- 
ditions, has been responsible for the 
rise of the talkie — the world's most 
popular form of entertainment. 

A moment's consideration of the 
multitude of new problems created by 
sound will bring appreciation of the 
versatility required to lift talking pic- 
tures to their present high standard. 
Directors and writers have been con- 
fronted with a maze of new problems. 
It is a tribute to them, as well as to 
the players, that the audible films of 
today are dominating the entertain- 

* Vice-President in charge of production 
of Radio Pictures. 

By William he Baron * 

ment field in this country and sweep- 
ing throughout the entire world. 

Some of the industry's best known 
directors and writers of the silent era 
have become outstanding successes in 
the field of talking pictures. In order 
to accomplish this it was necessary for 
them to change their entire conception 
of screen technique. Pantomine no 
longer sufficed ; audible films require a 
judicious use of action, voice, sound 
and music. Instead of appealing only 
to the eye of the spectator, the modern 
director and writer must present his 
story to the eye and ear. 

Entirely New Problems 

When Luther Reed directed "Rio 
Rita" and "Hit the Deck" he was con- 
fronted with numerous problems which 
never existed in the days of silent 
films. He worked in close collaboration 
with composers and lyricists, the 
musical director and his symphony 
orchestra, the choristers, and with the 
dance instructor who trained the scores 
of girls. He conferred with sound ex- 
perts and with them solved many prob- 
lems of recording dialogue, music and 
sound effects simultaneously. When he 
selected players, he had to choose those 
who could speak lines properly, sing 
and in some cases, perform specialty 

These are problems faced by every 
director of today. By the same token, 
writers have adapted themselves to a 
new medium of expression. Given a 
miraculous scientific device which re- 
creates living voices and sounds on a 
hitherto mute screen, it has devolved 
upon them to utilize it to depict drama, 
comedy, sorrow, happiness, romance, 
adventure and the many other elements 
which enter into the creation of screen 
entertainment. Such writers as James 
A. Creelman, Jr., Jane Murfin, Wallace 
Smith, Hugh Herbert and John Russell 
have recognized the possibilities of 
sound and are making the fullest use 
of it in Radio Pictures. 

Stage technicians and artists found 
a new avenue of enterprise opened to 
them. Because music and song play 
such an important part in modern films, 
artists like Victor Baravalle, R-K-0 
musical director, Harry Tierney, com- 
poser, Anne Caldwell, librettist and 
Pearl Eaton, dance director, have be- 
come more valuable to their studio. 

Of course, writers, directors, mu- 
sicians and the other creative minds 
behind the scenes have not been the 
only ones who found it necessary to 
make an adjustment. Film players, 
trained in the school of the silent 
screen, have taken cognizance of 

Change in R.C.A. Photophone Policy 

Three Types of Equipment to be Distributed 

THROUGH Charles J. Ross, 
executive vice-president, RCA 
Photophone announced recently 
a radical change of policy in 
connection with the distribution of its 
sound reproducing equipment. 

The high-lights of the announcement, 
which are of particular interest to ex- 
hibitors, were that the corporation 
would confine its activities to the dis- 
tribution of three types of sound re- 
producing equipment ; that the price 
heretofore established for equipment 
for theatres up to 500 seating capacity, 
would be the same for theatres having 
a capacity up to 1,000 seats and that 
the exhibitor will have the right to 
cancel, at his option, the obligation to 
receive and pay for service after the 
first two years. 
Prior to this time, RCA Photophone 

sound reproducing equipment for 
theatres above 500 seating capacity and 
up to 1,000 seats, had been nearly 
double the cost of the model known as 
Type G, which was designed for 
theatres having the smaller seating 

The three types of equipment to be 
distributed in accordance with the pro- 
visions of the new policy, have been 
given three classifications, — Type B for 
theatres above 2,000 seating capacity; 
Type C for theatres between 1,000 and 
2,000 capacity and Small Theatre Type 
for theatres up to 1,000 seating 
capacity. In the small theatre models 
the exhibitor may choose between 
battery or motor generator operation. 

"A few weeks ago announcement was 
made that RCA Photophone, Inc., pro- 
posed to embark upon a campaign of 

unprecedented expansion," said Mr. 
Ross, in discussing the corporation's 
new policy. "Activities in that direc- 
tion have been under way ever since 
and already the results obtained have 
far exceeded expectations. The re- 
sponse that immediately followed the 
introduction of the Type G equipment 
brought about the decision to fix the 
price for all equipment for theatres up 
to 1,000 seating capacity at the figure 
established for the Type G equipment, 
which was designed for theatres of 500 
seats and under. This marked reduc- 
tion in price to the larger of the two 
classes of theatres, was determined 
upon after many conferences as was 
the decision to give the exhibitor the 
right to cancel the provision in the 

(Concluded on page 28) 

Page 26 

Projection Engineering, March, 1930 


Their Character and Protection 
By Richards & Geier* 

THERE is 110 longer any question 
that a prosperous business 
should have some distinctive 
word or symbol — a trade-mark 
which will identify the products of 
the business, and when wisely em- 
ployed in advertisements and pam- 
phlets, will foster their sale. In many 
large business enterprises today trade- 
marks have been conspicuous factors 
in the expansion of the business and 
the increase of sales. Every once in 
a while you read of large sums being 
paid for "The good-will of the busi- 
ness including the Trade-Mark." Fre- 
quently the trade-mark is the most 
valuable asset in a business. Such 
notable trade-marks as "B V D," 
"KODAK," "COCA-COLA" are valued 
by their owners at princely sums of 
money, and are undoubtedly the most 
important asset in the business in 
which they are used ; one cannot 
imagine carrying on the business with- 
out the trade-mark. 

In the business of merchants and 
importers trade-marks have played a 
conspicuous part in the commercial 
development of the enterprises they 
serve. A trade-mark grows with the 
business, and, gaining celebrity with 
the passing years, places the business 
on a firm foundation which spasmodic 
business depressions will not be able 
to seriously affect. In times of stress 
and meagre profits the business whose 
trade-mark is a familiar sight to the 
public and the trade, will always en- 
joy some volume of business while the 
manufacturers or merchants who have 
not adopted a trade-mark to identify 
their goods are in a far less fortunate 

Sooner or later every expanding 
business invokes the aid of advertis- 
ing in one form or another. It is 
here where a trade-mark is almost in- 
dispensable since the article should be 
impressed upon the public mind 
through some definite symbol, or some 
expressive term which will impress it- 
self indelibly upon the public mind. 
The trade-mark must be sufficiently 
striking to linger in the memory of 
the purchaser if the advertising is to 
serve its purpose. 

This involves a discussion of the 
selection of appropriate trade-marks. 
Trade-marks are not only for experts, 
but for the public in general, which 
includes "the ignorant, the unthinking 
and the credulous, who in making pur- 
chases do not stop to analyze but are 
governed by appearances and general 
impressions." In the selection of a 
trade-mark of character, the habits 
and the intelligence of the purchasers 
should be considered. Thus, different 

* Patent and Trade-Marh Attorneys New 

circumstances should govern the adop- 
tion of a trade-mark for a product in- 
tended primarily for children, and an 
article destined for the adult trade. 
Particular care should be exercised 
by merchants and manufacturers who 
export, or import their wares. The 
trade-mark must be one that will easily 
be retained in the memory of the citi- 
zen of the country where the goods 
are sold. Thus, a manufacturer or 
merchant located in Germany who 
sells a market in the United States 
and other English speaking countries, 
should not select a trade-mark which 
could not be readily pronounced or 
remembered by those who speak 
English. Then again, a complicated 
Anglo-Saxon word trade-mark would 
be ill-chosen for the Spanish speaking 
countries of Central and South 
America, where a more simple but 
expressive word or symbol would best 

The proper protection of valuable 
trade-marks by registration is a sub- 
ject which even in these enlightened 
days does not receive the attention 
and consideration it deserves. A 
trade-mark, as soon as adopted and 
used, should be properly safeguarded 
by registration ; the cost of which is 
about Two to Five Dollars per year, 
when apportioned over the full time 
of registration. A trade-mark that has 
been registered may be marked with 
a notation to that effect, and this has 
a deterrent action on competitors who 
have a habit of simulating trade- 
marks. Any reputable manufacturer 
would hesitate to adopt a trade- 
mark which is identical with, or con- 
fusingly similar to a mark preempted 
by reason of its registration by an- 
other party. There are numerous 
benefits accruing from registrations of 
trade-marks under our Federal Law. 
Registration in the U. S. Patent Of- 
fice enables the owner of the trade- 
mark to sue infringers in the United 
States Courts. The registration of a 
trade-mark at Washington makes a 
public record of the owner's claimed 
rights, and serves to guide others who, 
in quest of a trade-mark, search the 
records at Washington. In a suit for 
infringement of a trade-mark regis- 
tered under the Trade Mark Act of 
1905, registration in the Patent Office 
at Washington is accepted by the Court 
as prima facie evidence of ownership 
of the mark. In the event a trade-mark 
suit is successful, the Federal Court is 
empowered to grant an accounting of 
the infringers profits to be paid to the 
owner of the trade-mark, together with 
the damages sustained by reason of the 
infringement. Furthermore, registra- 
tion of a trade-mark in the United 
States is a prerequisite in many 

countries, when an American merchant 
or firm seeks registration of its trade- 
mark abroad. 

This leads to a discussion of the 
protection of trade-marks abroad. In 
a great many countries outside the 
United States, the first one to register 
a trade-mark is regarded as the owner 
thereof. In many instances the failure 
of manufacturers or merchants to regis- 
ter their trade-mark under the laws 
of a particular country has resulted in 
the appropriation and registration of 
the mark by some agent or trade-mark 
pirate who has then demanded substan- 
tial sums from the owner of the mark 
before they would return the same. 
Since in many countries the registrant 
of the mark may prevent the entry of 
goods bearing the same mark, some 
agreement with the trade-mark pirate 
is necessary. In a number of cases the 
trade-marks of American manufac- 
turers have been registered in Central 
and South American countries by the 
agent of the manufacturer, thus mak- 
ing the agent the owner of the mark, 
and placing him in a position to per- 
petuate his agency, as well as com- 
pelling the American manufacturer to 
agree to his terms. For this reason 
American manufacturers, or those of 
other countries, should without delay 
register their trade-marks in all coun- 
tries to which their trade extends, or 
where it is likely to extend. 

A trade-mark may be a word, sign, 
emblem or combination of these ele- 
ments. It must be distinctive, and 
either by itself, or by association and 
use, indicate the origin or ownership 
of the goods to which it is attached, 
so that it will perform its function of 
distinguishing the owners goods from 
those of other persons. A trade-mark 
is an asset — an integral part of the 
good-will of the business. Trade-marks 
are intended to be attached to articles 
of merchandise and their special func- 
tion is to indicate origin or ownership 
of the goods to which they are applied. 
The use of a trade-mark does not 
necessarily imply that the articles upon 
which it is used are manufactured by 
the owner of the mark. It may be that 
they are manufactured for him, or that 
he controls their production — what is 
necessary is the actual sale of articles 
by the owner, accompanied by labels, 
tags or other suitable specimens show- 
ing the trade-mark. It is clear, there- 
fore, that a jobber, wholesaler or re- 
tailer may be the owner of a trade- 
mark. An example will illustrate our 
point ; very often a wholesale dealer in 
garments does not manufacture him- 
self. A contractor performs the service 
for him. The wholesaler, however, 
applies his own trade-mark to the 
garments and sells them to the 

Projection Engineering, March, 1930 

Page 27 

trade. His trade-mark is accepted 
as the indication of their source, 
and as such is entitled to pro- 
tection. A retailer may adopt a 
trade-mark and attach it to all goods 
sold by him. The circumstance that 
the goods also bear the trade-mark of 
the manufacturer would not affect the 
retailer's right to apply his trade-mark 

All trade-marks must be attached in 
some way to the goods, or the con- 
tainers of the goods. The manner in 
which a trade-mark is applied 
or affixed to the goods, or the 
containers thereof is immaterial. 
They may be printed, impressed, 
moulded, cast or otherwise applied 
to the goods or they may be 
affixed to the goods or the packages 
containing the goods by means of a 
label, plate, tag or other suitable de- 
vice. The mode of application of a 
trade-mark will always be governed 
by the particular commodity involved. 
A trade-mark may be directly im- 
pressed upon soap, but it could not be 
directly impressed upon a liquid, i. e., 
hair tonic. In the latter case the 
trade-mark would be printed or re- 
produced upon a label which would 
be attached to the bottle containing 
the tonic. In some instances the trade- 
mark may be applied by means of 
aecaleomania transfer signs. All that 
tne law requires is that the trade-mark 
accompany the goods in commerce 
— how it accompanies the goods is 

To entitle a trade-mark owner to 
Federal registration the actual use of 
the trade-mark in interstate commerce 
is necessary. Mere adoption of a 
trade-mark, with intent to use it in 
the future, will not create any trade- 
mark right until the mark is actually 
used. It is not necessary that the mark 
should have been used for any definite 
or considerable time, and a single 

actual use confers a right to such 
trade-mark, if the article with 
the mark upon it has actually 
become a vendable article in the 
market, with the intention of the 
proprietor to continue its production 
and sale. The use of a trade-mark on 
letter-heads, pamphlets and stationery 
would not create any trade-mark 
rights under the laws of the United 
States, since letter-heads, etc., do not 
accompany the trade-mark in inter- 
state commerce. 

The basis of a trade-mark right in 
the United States is priority of adop- 
tion and actual use in trade. The first 
one to use a given trade-mark upon a 
particular class of goods acquires the 
prior and exclusive right upon that 
general class of goods ; however, an- 
other person may apply the same trade- 
mark to an unrelated and different 
class of merchandise. The use of a 
trade-mark must be bona fide, and not 
merely for the purpose of coming with- 
in the letter of the trade-mark law. On 
the other hand, a trade-mark right is 
not lost through non-use due to fire, 
war or other causes which do not 
imply an intention to abandon the 
mark. To establish abandonment of a 
trade-mark, there must be an actual 
intention permanently to give up the 
use of the mark ; in the absence of 
such intention, mere non-use though 
for a considerable period, will not 
amount to abandonment, nor destroy 
rights acquired in the mark. 

Perhaps it would be well to add a 
few words as to the procedure to be 
involved when a merchant or manu- 
facturer adopts a trade-mark. After 
the manufacturer or merchant has 
selected the mark it would be well to 
consult some competent Patent and 
Trade-Mark Attorney, and authorize 
him to make a search in the U. S. 
Patent office to ascertain whether any- 
one else has registered the same trade- 

mark, or a close or similar trade-mark 
for the same class of goods. This 
should be done before the owner incurs 
any expense in connection with the 
production of labels, advertising, etc. 
There have been too many instances 
where manufacturers or merchants 
have spent thousands of dollars upon 
labels and advertising a mark, only to 
find that someone else had already 
registered the same for similar 
goods. If the trade-mark search does 
not disclose any prior registrations, 
then the trade-mark application should 
be proceeded with and some labels 
should be made up. Some goods should 
be sold in interstate commerce, accom- 
panied by labels and the trade-mark 
application should be filed and prose- 
cuted with a view to securing its 
ultimate grant at the earliest possible 
time. The Trade-Mark Law is such 
that the final grant of a trade-mark 
usually takes from four to eight 
months from the time that the 
application is filed in the Patent 
Office. The procedure is somewhat 
complicated by the machinery set 
up by the Law, which requires 
the Examiners in the Patent Office to 
closely examine trade-mark applica- 
tions and reject the same where they 
are not in proper form, or where the 
same trade-mark has been registered 
by someone else previously. Even 
after the Examiner passes the appli- 
cation as allowable it must first be 
published in the Official Gazette of the 
United States Patent Office, and a 
period of thirty days must elapse from 
such publication before the trade-mark 
is prepared for final grant. This 
thirty day period, from the time of 
publication, is for the purpose of per- 
mitting competitors and other inter- 
ested parties to file protests or op- 
positions, if they feel they have any 
ground to do so. 


DUE to the modest amount of 
detail obtained with present 
television methods, it seems 
certain that radio television 
will be accompanied by synchronized 
voice or music, thereby obtaining what 
may be termed "radio talkies." The 
relatively perfect sound accompaniment 
must go far towards preventing the 
audience from concentrating on the 
pictures themselves, and also in ex- 
plaining the action so as to make the 
story more enjoyable. 

At least such is the opinion of J. E. 
Smith, President of the National Radio 
Institute of Washington, D. C. "It is 
relatively simple," states Mr. Smith, 
"to provide radio talkies. The sound 
accompaniment may be transmitted 
over any broadcasting station, while 

the radiovision signals may be trans- 
mitted by a television transmitter. 
Working from actual subjects or again 
from sound pictures, the picture sig- 
nals are transmitted on the radiovision 
short waves, and the sound signals on 
broadcast waves. At the receiving end, 
a standard broadcast receiver tunes in 
the sound accompaniment, while a 
short-wave receiver and radiovisor 
handle the pictures. 

"But for the ingenious combination 
of sound and picture signals, I do not 
believe that radiovision programs 
would have much entertainment value, 
once the first curiosity of the public is 
satisfied. However, as radio talkies, 
the attraction is certain to last until 
such time as a better radiovision 
technique is forthcoming." 


200 kilowatts of power was first put 
on the air for broadcast purposes 
Sunday morning, March 9, at 4 o'clock 
E. S. T. by WGT, the General Electric 
Company station at Schenectady, N. Y. 

Operation under special license 
W2XAG has been authorized by the 
Federal Radio Commission. 

The transmitter employs a 200-kilo- 
watt linear power amplifier, incorpo- 
rating in a push-pull circuit, six-super- 
power radiotrons which are conserva- 
tively rated at 100 kilowatts each. 

The high power station uses a verti- 
cal cage antenna and radial counter- 
poise. Antenna current is 92 amperes. 

Frequency control is maintained by 
piezo-electric crystal. W2XAG operates 
on 790 kilocycles or wavelength of 
379.5 meters. 

Page 28 

Projection Engineering, March, 1930 


(Concluded from page 25) 

contract pertaining to service. Now, 
upon sixty days notice, after two years, 
the exhibitor may exercise his option 
to annul the service clause in the 

"In the three classes of equipment 
henceforth to be distributed by RCA 
Photophone, Inc., exclusive, of course, 
of the new portable machine that has 
just been introduced, we cover any 
type of theatre and any seating 
capacity. Because of existing con- 
ditions, due to the fact that the ma- 
jority of the first and second-run 
theatres in the country have been 
wired, it will be our purpose to con- 
centrate our activities upon the dis- 
tribution of the small theatre equip- 
ment. Nearly 200 models of that type 
have been contracted for and shipped 
to exhibitors within the past thirty 
days and with the release of the 
announcement that 1,000-seat houses 
may acquire that equipment at the 
price the 500-seat house has been 
paying, we view the future with keen 
anticipation. We are prepared, how- 
ever, to meet any emergency, for we 
have determined to take our rightful 
place at the head of the procession of 
reliable sound equipment distributors. 
And it seems to me that the provisions 
incorporated in RCA Photophone's new 
policy, warrant the issuance of that 
pronouncement. We firmly believe in 
the corporation's product and in arriv- 
ing at the provisions in the new policy, 
gave careful consideration to the needs 
of the exhibitor." 



EMPLOYEES of the research de- 
partment of the Radio Corpora- 
tion of America have been trans- 
ferred to various subsidiary 
companies. A number of the men have 
gone to the engineering department of 
RCA Victor at Camden, some to the 
engineering products division of the 
sales department of RCA Victor in 
New York, others to the NBC and RCA 
Communications and still others to 
RCA Photophone, Inc. 

The Photophone company has organ- 
ized a research group in its engineering 
department, a number of the employees 
of the research department of RCA 
being transferred for this purpose. The 
work is being directed by Julius Wein- 
berger, formerly engineer-in-charge of 
the RCA research department. The 
group consists of Messrs. Korman, 
Kreuzer, Malter, Maurer and Olson, 
with Miss Beatrice Schrag as secretary. 
This group will carry on advanced re- 
search in all of the fields in which 
RCA Photophone is interested, par- 
ticularly in sound motion picture re- 
cording and reproduction. 

Jac. R. Manheimer 

I WAS a passenger on the S.S. Duilio 
of the Navagazione Generale 
Italiana Line, which arrived in 
New York port on Saturday, 
March 17, 1928. 

On Wednesday night, March 14th, at 
about 11 p. m., near the end of the 
showing of a moving picture in the 
music salon on the forward upper deck, 
a fire broke out in the picture booth. 
The booth was located under the bridge 
on the forward part of the same deck. 
From what I could learn the Are was 
started by the film in the machine 
igniting at the aperture plate. 

In a very short time the entire in- 
terior of the booth was aflame, being 
constructed entirely of wood, and one 
of the operators was badly burned 
about the face and hands. There were 
about three of the crew on duty, and 
while the officers on the bridge must 
have known of the fire, since they were 
directly over it, no fire signal was 
given, in order. I believe, not to alarm 
the passengers, many of whom had 
retired for the night. 

When the fire broke out I believe the 
operator in the booth tried to use a 
fire extinguisher, which was of a low 
wide-can type of presumably Italian 
make, but this did not operate. One 
of the other passengers called my atten- 
tion to the fire and I ran forward and 
saw three of the crew trying to unravel 
and untwist a 50-ft. line of 2-inch hose 
which was previously in a cabinet 
having a glass door and which was 
coiled up, but without a reel. In their 
attempt to hurriedly unsnake the hose 
they pulled the inside out of it first, 
with the result that the entire hose 
was twisted and they could not get 
water through it. I helped them try 
to unravel the hose, but very little 
progress was made, so I ran to the 
other side of the ship, broke the glass 
on a cabinet and rolled out the hose I 
found there by laying it on the floor 
and unrolling it as one would a carpet. 
I finally connected the hose to the hose 
bib on the stand-pipe and had water up 
to the picture booth before the crew 
on the other side of the ship were able 
to disentangle their hose. 

The fire reached what I thought to 
be tremendous proportions, as the 
entire booth was aflame and the six 
reels of film probably added to the 
combustion to such an extent that it 
broke the %-inch plate glass storm 
window directlv in front of the booth 
on the lower bridge. At this time there 
was a 60-mile gale blowing, it being 
one of the stormiest nights we had at 
sea, and the fanning effect of this gale 
probably aggravated the fire. 

Through the presence of mind of one 
of the other passengers the transom 
through which the pictures were being 
projected to the music salon was closed 
by someone getting up on a chair and 
pushing the transom shut, which prob- 
ably averted a panic as well as serious 

rN.F.P.A. Quarterly. 

damage to the ballroom and probably 
the rest of the ship. 

The fire was finally extinguished. 
In order to discount the seriousness of 
the fire, the crew replaced the damaged 
machine with another machine which 
they had taken out of the Second 
Cabin, and were ready to show pictures 
the following night, except that the 
First Class passengers got together and 
protested to the purser that no more 
pictures be shown on this trip. 

When this fire occurred we were 
nearly 2,000 miles from shore on a very 
stormy sea, the fire extinguishers ap- 
parently did not work, the crew did not 
know how to handle the hose expe- 
ditiously, and worst of all, a wooden 
picture booth was used which was 
probably improvised recently by plac- 
ing it on this bridge and projecting the 
pictures through the transom. The 
moving picture machine head and lamp 
house were both mounted on a wooden 
pedestal. No safety cans were pro- 
vided for the films not in use, and no 
self-closing fire shutters, which would 
have closed the transom through 
fusible links, as is customary. 

It seems to me nothing less than 
criminal to expose the lives of about 
2,000 passengers to a hazard such as 
this when the Government uses every 
precaution to see that life boats are 
properly provided and equipped, and 
film fires are certainly of more fre- 
quency than other distressful con- 
ditions of the sea which would require 
life boats. 


AN entertainment novelty intro- 
duced to the public in New 
York City seventeen years ago, 
on Monday afternoon, Febru- 
ary 17, 1913, gave little, if any, evi- 
dence that it was the forerunner of 
a revolutionary change in motion pic- 
tures. But on that date combined sight 
and sound was projected by means 
of a device called the kinetophone, 
perfected by Thomas A. Edison. It 
was more than a device — it was two 
devices, the motion-picture projector 
and the phonograph. A belt ran from 
the motor of the projection machine 
to a phonograph behind the screen, 
operating them together. For a short 
time it amused audiences, but it was 
looked upon as an oddity and soon 
was removed from the market. Little 
was heard of talking pictures after 
that until about 1925, when it became 
known that a motion-picture company 
had acquired the rights to a newly 
perfected sound recording and repro- 
ducing system. In 1926 the first of 
the new type of talking pictures was 
shown publicly. For the pioneer talk- 
ing picture of 1913 a phonograph rec- 
ord was made first of the actor's 
voice. Then as the record was played 
the actor sang or talked again, this 
time for the camera. When the action 
was in fairly good synchronization 
with the reproduced voice, the talkie 
was completed. 

Projection Engineering, March, 1930 

Page 29 

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Clear, realistic pictures, freedom from eye-strain, and natural tone quality 

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To insure projection a9 good as you had before Sound, to get the best 

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SERVICE MEN use more 
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INTERNATIONAL RESISTANCE COMPANY. .7006thestnui Si. Philadelphia, Pa. 

S-A-F 3 ( 




assures complete 
sound control 

Your patrons demand 
the best in "Talkies" — 
you can give it to them 
with S-A-F 3 equip- 
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easily installed, and 
simple to operate. A 
mere turn of a knob 
eliminates the unnatur- 
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shrillness in notes and 
the unpleasantness and 
echoes of sounds. Your 
audience will be grate- 
ful for this improve- 
ment — and your box 
office will be busier! 

SAF Electrical Equipment Co., Boston, Mass. 

S-A-F 3 was designed by Simpli- 
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groups of engineers in the talking 
equipment industry — they have always 
led in offering improvements! Send 
the coupon below for complete in- 
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Gentlemen: Kindly send me free bulletin on S-A-F 3 and place my 
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leading engineers, professors and experts. 


Address . . 

Page 30 

Projection Engineering, March, 1930 

New Developments 


News of the Industry 


The SAF 3, manufactured by Simplimus, Inc., 
Boston, Mass., is one of the most important advances 
in natural reproduction of sound since the advent 
of the talkies. 

The SAF 3 is built to correct most of the defects 
encountered in present-day reproduction. It is de- 
signed to add brilliance and depth to reproduction. 
It will make the voice sound more natural and human, 
and the music more pleasing. 

When playing an orchestra recording, the SAF 3 
can take out the base horn without affecting the 
higher pitched instruments. It can also take out 
the high, shrilly notes without affecting the lows. 

In voice reproduction the SAF 3 will eliminate 
the low drummy sounds which muffle the speech, and 
it will bring out the high frequencies necessary to 
clear articulation and pronunciation. 

Full instructions how to attach accompany the 
SAF 3. It can be connected in a few minutes. 
Deliveries are immediate. 

The SAF 3 Mixer will work with all makes of 
amplifiers and all makes of talking equipment. 


The Interstate Electric Company, 4339 Duncan 
Ave., St. Louis, Mo., manufacture rectifiers suitable 
for recharging storage batteries used in connection 
with talking-picture equipment. These chargers can 

be used on 3, 5 or 6 cell batteries at either a 
6 or 12 ampere charging rate. They set up no noise 
in the amplifying equipment, being of the 2-coil 
type, full transformer. 


A new striper, for continuous striping with lacquer, 
paint and aluminum bronze has been brought out by 
the Paasche Airbrush Company, 1909 Diversey 
Parkway, Chicago. . 

This striper has many uses in the manufacturing 
industries, making for improved appearance of products 
and for economy in production. 


The Sauter Time Switch automatically turns lights 
"on" and "off" at predetermined hours. It is used 
by theatres for control of their sign lighting, marquee 
lighting, flood lighting, and by larger theatres where 
airway and roof marker signs have been installed. 

This time switch is marketed by R. W. Cramer & 
Company, Inc., 136 Liberty St., New York City. 

A small motor winds the clock and operates the 
switch with very little electricity cost a year, and it 
Is said to pay for itself by watching that no unneces- 
sary lighting is wasted. 


. Electrical Research Products has closed contracts 
for the installations of Western Electric Sound Sys- 
tems at the offices of the New York Censor Board 
in 42nd Street, New York, and in the Army Y. M. 
C. A., at Fort Jay, Governor's Island. The stand- 
ard 3S equipment is being used for both installations. 

Hie conscientious, overworked tire marshal who is 
doing so much running around these days trying to 
minimize the fire hazards attendant upon the hanjling 
of motion pictures, is receiving material aid from 
the Hewes-Gotham Company who have developed a 
fireproof film cement. 

In addition to its fireproof qualities which have 
been tested and approved by fire prevention bureaus 
of several states all over the country, the new cement 
continues to carry the "2-in-l" feature of the com- 
pany's film cements. Both the standard nitrate and 
the safety non-flam films can be spliced with it. 


A newly developed enamel of superior qualities is 
used in the manufacture of the wire-wound resistance 
units made by The Cresradio Corporation. The coating 
has the same coefficient of expansion as the wire used. 
This company's Crescent Lavite resistances have been 
on the market for the past seven years. 

The Kinoplay Corporation, 1600 Broadway, New 
York, has issued a new catalog of its Multiphone 
(sound-on-disc) and Kinoplay (sound-on-film) ap- 
paratus. This synchronous equipment is applicable to 
Powers, Simplex, Motiograph, Superior and standard 
European projectors. 


A line of optical crown glass plates for inclosing 
projection and observation portholes in projection 
booths, is being marketed by the Fish-Schurman Cor- 
poration, 45 West 45th Street, New York. 

The introduction of the Filmo 75 Camera to the 
American movie-making public quickly brought the 
demand for Super-Speed lenses. Long distance and 
telephoto lenses for the "75," which make distant 
subjects "close-ups," are listed in a new catalog 
issued by Bell and Howell, 1801-15 Larchmont Ave- 
nue, Chicago, Illinois. 


One of the outstanding features of the Chicago 
Radio Show is the first commercial home televisor, 
which was demonstrated at the DeForest Radio Com- 
pany's booth. This device is an actual production 
model of the Jenkins Television Corporation, and 
represents the type of equipment which will soon be 
available to the public. 

Briefly, the Jenkins televisor is a handsome wooden 
cabinet measuring about 18 by 18 by 24 inches. The 
front panel contains a recessed opening or shadow- 
box, through wh ; ch the pictures can be viewed. A 
magnifying lens in the shadow-box enlarges the radio 
pictures so that as many as eight persons may view 
them at one time. Directly below the shadow-box 
opening is a metal panel with two toggle switches, 
one to control the "loudspeaker" and "picture" 
functions, and the other to start, accelerate and 
stop the motor 


The Jenkins televisor must be employed in com- 
bination with a short-wave radio receiver to tune 
in the television signals, and a suitable amplifier to 
amplify the signals without introducing distortion. 
In actual operation, the top televisor switch is thrown 
to the "loudspeaker" position, and the characteristic 
buzz-saw signals are tuned in as loudly as possible. 
The switch is then thrown to the "picture" position, 
while the motor switch starts the motor. The 
pictures are then viewed in the shadow-box, in the 
form of pink-and-black animated pictures. If the 
pictures are out of frame, the motor switch is flipped 
until the pictures are properly framed. 

The present device is said to be entirely com- 
mercial and intended for immediate use in the aver- 
age household. 


World-wide installations of Western Electric Sound 
Systems are nearing the 5,000 mark. The latest 
report shows that 3,489 installations have been com- 
pleted in the United States and 1,268 in the foreign 

The 500th installation of a Western Electric 
Sound System in the British Isles has just been 


An announcement of exceptional interest to elec- 
trical laboratories and manufacturers making electri- 
cal apparatus is the variable voltage test ng trans- 
former, an entirely new departure in the transformer 
field. This transformer is a development of the Don- 
gan Laboratories, as the result of an insistent 
demand from various engineers for this type of trans- 

By the use of this transformer, an electrical labora- 
tory or manufacturer can definitely fix upon any volt- 
age within a range of 1 to 150 volts in steps of one 
volt with input of 115 volts. Thus, all guess work 
can be eliminated in the designing of electrical 

The findings of the proper voltage is quick and 
simple. There are two plugs and twenty-five outlets, 
one plug controlling the voltage in one-volt gradua- 
tions, and the other plug in 10-volt graduations. The 
current capacity is 5 amperes at any voltage. 

A feature of this variable voltage testing trans- 
former is the fact that all connections are designed 
to eliminate the possibility of accidental short cir- 
cuits or shocks. 

Mounted in a polished walnut case with an engraved 
bakelite panel, the transformer weighs 14% lbs. It 
is made for either 60 cycles or 25 cycles. The 
specification number is 4612. 

Designed and manufactured by the Dongan Electric 
Manufacturing Company of Detroit. 


As a result of the formation recently of a "foreign 
production committee" through the medium of the 
Academy of Motion Picture Arts and Sciences, repre- 
sentatives of various film studios are cooperating in a 
movement to solve the problem of converting American 
talking_ pictures into the native tongues of the foreign 
countries in which they are exhibited. 

This problem, it is said, is one of the most crucial 
facing the cinema industry today, involving the preser- 
vation of the great percentage of revenue on American- 
made pictures that heretofore has been derived from 
foreign markets. 

Various experiments have been tried to determine 
a feasible method of making talking pictures in the 
languages of other countries and it is the purpose of 
the committee, newly formed through the Academy, to 
arrive at a simplified and standardized procedure on the 

The committee's preliminary activities, which will 
be executed with the cooperation of the Academy, will 
cover, according to present plans, an interchange of 
all information touching foreign areas; collective view- 
ing of other studios' pictures; and assembling of 
authoritative data on abilities of linguists and foreign 
technical directors. 

Among the fields of foreign languages quoted in the 
Academy meeting were Spanish, French, German, 
Czech, Polish, Hungarian and Italian. 

Paul Kohner, of Universal Studios, was chosen as 
chairman, and Geoffrey Shurlock. of Paramount, as 
secretary, of the committee. Additional members in- 
clude John Stone, head of foreign department. Fox; 
Frank Davis, Jerome Lackenbruck and Salvador de 
Alberich, Metro -Goldwyn-Mayer; Leon d'Usseau, 
R-K-O, and Heinz Blanke and DeLeon Anthony, 
Warner Brothers. Lester Cowan. Assistant Secretary 
of the Academy, represented the Academy at the 


During the past year a new and highly lucrative 
field has been opened to the radio-trained man in 
the form of sound apparatus and installations. In- 
stead of merchandising non-descript amplifiers, pick- 
ups, wiring and loudspeakers, the trend today of the 
radio industry is to seek sound specialists or dealers 
in sound, who sell a complete sound installation and 
service rather than so much equipment. 

"Sound installations are in demand for all kinds 
of institutions, ranging from the school, church, pub- 
lic auditorium, park, and stadium, to the club room, 
hospital, railway waiting room, train platforms, and 
hotels," states J. E. Smith, president of the Na- 
tional Radio Institute of Washington, D. C. "Be- 
cause of the considerable investment represented by 
such installations, the public as well as the indus- 
try are prepared to deal only with radio-trained men. 
Many manufacturers of such equipment are seeking 
men who are willing to specialize in this lucrative 
field, and master the technique of acoustics as well 
as radio. Many organizations are coming into exist- 
ence in this field." 

Projection Engineering, March, 1930 

Page 31 





Powers Projector With S. S. White Flexible Shaft Drive 

Our success in applying flexible shaft drives to various 
types of cameras, projectors, turn tables and printers, 
warrants your consulting us on the possibility of supply- 
ing you with a flexible shaft drive for your equipment. 

The advantages of a flexible shaft drive over other types 
of drives are obvious ; ease of installation and flexibility 
being of paramount importance. 

Manufacturers and users of equipment listed above are 
invited to consult us on their flexible shaft problems. 
Copies of a paper on the "Application of Flexible Drive 
Shafts to Sound Picture Equipment," will be forwarded 
on request to those interested. 


A "Flexible Shaft Handbook" of 120 pages profusely 
illustrated and containing Detailed Information and 
Engineering Data on the Flexible Shaft. 

To any engineer, machine designer or executive respons- 
ible for machine design, a copy of the Flexible Shaft 
Handbook will gladly be sent without charge or obligation. 
We make only this reasonable condition; — that your 
request be made on your business letterhead and that 
you indicate your position. 

Write NOW for your copy. 



154-A West 42nd Street New York, N. Y. 

Manufacturers of SSW "Guaranteed 

Noiseless" Molded Resistances for 

audio amplifiers and radio receivers. 

Write for information. 

^ FORWARD... ^ 

0" g.< 




THESE television tubes are of proved per- 
formance and dependability. The Eveready 
Raytheon Kino Lamp, for television reception, 
is the first tube developed commercially that 
will work with all systems. Its glow is uni- 
form over the entire plate. Its reproductive 
qualities are perfect — without the need for 
mirrors or ground glass. Each tube is tested 
in our laboratories. 

The Eveready Raytheon Foto-Cell is a 
long-life transmitting tube for talking pic- 
tures and television. It is made in several 
standard types, and will be furnished to spe- 
cial specifications at reasonable prices. 

If you are interested in talking pictures or 
television — write to us. 


General Offices: New York, N. Y. 
Branches: Chicago Kansas City New York San Francisco 

Unit of Union Carbide | J \ ? '< J and Carbon Corporation 



Page 32 

Projection Engineering, March, 1931} 


Since the inception of the "talkies" realism has 
been the order of the day. From the gilded palaces 
of the Great White Way to the town hall in the 
smallest hamlet, "louder, sweeter and clearer, please" 
is the sentiment if not the cry of the populace. 
Technical achievement has gone far to gratify this 
demand. There are of course exceptions to this rule 
of progress; science has never been able to render 
electrical or mechanical equipment absolutely immune 
to breakdown and trouble. It has, however, been 
able to perfect the component parts of an assembly 
to the point where a reasonable amount of trouble- 
free service may be taken for granted. 

In the average theatre today sound is reproduced 
with maximum volume and minimum distortion. 
Furthermore, this flawless service is assured over a 
relatively long period of time. The day of the con- 
verted and glorified radio assembly in sound work 
is over. Loudspeakers are being designed especially 
for the great spaces that they must fill with undis- 
torted sound and the loads that they must carry. 
Amplifiers are being built along battleship lines with 
enormous safety factors to assure permanent, trouble- 
free service. 

Only one serious problem has blocked the path of 
perfect, steady, reproduction. As in so many indus- 
tries, it has been the variable factor. A chain is 
said to be no stronger than its weakest link. In 
science the weak link is the variable factor. Auto- 
mobiles, are built with the assumption that they are 
to be driven on fairly good roads. They are not de- 
signed to climb rocks or cross swamps. The use to 
which the car is put, however, remains the variable 
factor, over which the builder has no control. 

A variable factor has also been discovered in sound 
reproduction. Like the automobile designer, the elec- 
trical equipment designer has taken for granted the 
road upon which the machine is to be used; namely, 
the current supply upon which the device is to be 
operated. Most electrical equipment, unless other- 
wise specified, is designed to operate on 110 volts 
alternating current. However, it has been discovered 
that the so-called 110 volts may vary anywhere be- 
tween 90 and 130 volts, depending upon the locality, 
load upon the line, transformer equipment, time of 
day, and other factors beyond the control of the 
power company and the designer of the apparatus. 
Thus the actual voltage applied to a sound amplifier 
may vary within wide limits, either momentarily, due 
to a sudden heavy load upon the line, or steadily as 
in the case of a voltage drop due to a long trans- 
mission line. 

Vacuum tubes operating below the specified voltage 
provide poor tone quality and weak volume. High 
line voltage, on the other hand, may result in a short 
but brilliant performance. The load being much 
greater than that for which the equipment was de- 
signed, resistors, transformers and vacuum-tube fila- 
ments are subject to burn-outs. 

With the realization that current fluctuation is the 
rule and not the exception came the necessity for 
providing some means by which a definite current 
supply of constant voltage could be maintained. In 
the development of a device to solve this problem 
resistance was called upon to play a most important 
part. The device was called the line ballast, since 
it throws the weight one way or the other to com- 
pensate for any voltage fluctuation. 

If the line voltage only dropped, it might be com- 
pensated for by the use of properly designed low- 
voltage transformers. Unfortunately, however, line 
voltages rise as frequently as they drop, making it 
impossible to employ low-voltage transformers, since 
any increase above normal would seriously overload the 
tubes and result in disrupted service. The tapped 
transformer with a choice of two voltage ranges, 
adopted by some equipment manufacturers, was a 
half-way improvement. It was a relief measure, but 
by no means a cure, being unable to cope with line 
voltage fluctuations. Automatic and instantaneous 
regulation was necessary for complete satisfaction. 

Rather than discuss further the qualifications of a 
voltage regulator, let us analyze the device that has 
been perfected and is in operation at the present 
time. The Garostat line ballast operates on the 
automatic compensation principle of a series resistor 
with a high temperature coefficient, so wound and 
ventilated that a change in line voltage is instantane- 
ously compensated for by a change in the resistance 
value of the ballast. A constant voltage is main- 
tained on the transformer primary, even though the 
line voltage varies as much as 30 per cent, up or 
down. During this wide voltage fluctuation, the 
primary voltage, and consequently the secondary volt- 
age of the transformer, varies less than the plus or 
m'nus 5 per cent limit specified by vacuum-tube 

In this form of equipment the power transformer 
and the line ballast are matched, or designed to func- 
tion together. If the average line voltage to be dealt 
with is 110 volts, the primary of the power trans- 
former is designed for operation at 85 volts and the 
difference in voltage between this and the line is 
built up across the line ballast. Even though the 
line voltage changes within the limits of 100 and 
130 volts, the transformer primary will never receive 
more than 89 volts nor less than 81, which figures 
are within the 5 per cent leeway allowed by vacuum 
tube manufacturers. The seund reproduction will 
remain stable. Neither blasts nor whispers will de- 
tract from the quality of the performance. 

Several types of line ballast, all intended for 
the same purpose, but of different design are on the 
market. Some cover wide limits, but are sluggish 
and permit a slight shock on the tubes. Some are 
active but do not cover wide enough limits. And 

others advertised as "ballasts" are nothing more than 
small fixed resistors mounted on a plug-in base, pre- 
venting overloading of the tubes but by no means 
compensating for weak voltage or acting as a ballast. 
The ballast is essentially a built-in proposition to be 
incorporated as standard equipment by the manufac- 
turer of the apparatus. Just as we look for ABC 
bearings and XYZ axles in the purchase of a motor 
car, so it is well to make sure that the proposed 
amplifier carries a device on the order of the Clarostat 
line ballast. 

The line ballast is but one of the many uses to 
which resistance has been put in sound work. Small 
wire-wound fixed resistors and heavy-duty variable con- 
trols all have duties of their own to perform in the 
sound outfit. Incorrect grid bias, incorrect plate 
voltages, incorrect input and output voltages, incor- 
rect volume control, these and many other allies of 
the demon, distortion, have been corrected in the 
perfectly constructed amplifier and sound installation, 
through the proper application of well-designed and 
well-conceived resistances. Thus resistance when prop- 
erly applied, might well be a synonym for that im- 
portant attribute of the talkies— REALISM. 


The Fox Hearst Corporation of New York, Com- 
mercial Division, licensed by Western Electric Com- 
pany to produce Movietone Talking Pictures for com- 
mercial and educational purposes, has appointed the 
Wilding Picture Productions, Inc., of Detroit, as their 
exclusive sales and production representatives for nine 
Central West states. A branch office is established in 
Chicago, and others will be opened in the near future 
at stragetic points to keep pace with the expansion 
in the use of commercial Movietone motion pictures. 

This appointment has been made in recognition of 
the important part Wilding Picture Productions, Inc., 
has played in introducing this new medium of com- 
munication to the industrial enterprises of the Cen- 
tral West. Among the many nationally known insti- 
tutions who have utilized Fox Hearst Movietone pro- 
ductions in their sales promotional and educational 
work, are such familiar names as Studebaker, Graham- 
Paige, Dodge Brothers, M'ajestic Radio, International 
Harvester Company, Chicago Daily News, Standard Oil 
Company, Western Union, Vogue Magazine, Indian Re- 
fining Company, Armour & Company, National Elec- 
tric Light Association, Chevrolet, the United States 
Army and the American College of Surgeons. 

Mr. N. E. Wilding, President and General Man- 
ager of the Wilding Picture Productions, Inc., as- 
sisted by X. F. Sutton, is in charge of the commer- 
cial Talking Picture activities of this organization. 


A study of photoplay likes and dislikes made by 
a college professor with 500 subjects shows, in re- 
sponse to the question: "What kind of pictures du 
you like best?" the following results: 

General College 

public, student, 

Per cent Per cent 

Comedy 20 25 . 

Melodrama 20 18 

Historical 21 17 

Mystery 15 23 

Sex drama 15 8 

Hestern 5 6 

Costume 4 3 

Thirty-seven per cent of those questioned preferred 
going to the cinema on Saturday. Forty per cent liked 
afternoon performances and 60 per cent evenings; 72 
per cent preferred the orchestra and 28 per cent the 
balcony. Of those who cited the balcony, one-half 
said that they preferred it because of economy and 
one-half because of a better view. One out of every 
four said he went to see a certain picture because 
of the star and three out of every four because of 
the photoplay itself. 

In response to the question: "What interests you 
most in pictures?" the classification was as follows: 

General College 

public, student. 

Per cent Per cent 

Stories 37 17 

Stars 26 12 

Entertainment 8 17 

Acting 7 16 

Life 5 10 

Romance 5 6 

Scenery 4 6 

Education 2 2 

Feature 5 2 


Tile second German-produced talking film to be 
exhibited in the United States. "Why Cry at Part- 
ing," was put on at the Fifth Avenue Theatre, 
New York, late in January. 

Critics who viewed and listened to the projection 
state that the picture is too long, taking up an hour 
and a half. One critic was of the opinion that 
"the voices are not particularly well synchronized. 
The tonal quality is natural, but the speech impresses 
one as being delivered from a distance and then 
amplified. It sounds muffled. Sometimes it is difficult 
to decide who is talking, and the male voices are 
unusually high pitched. In one episode the singing 
is better recorded than the talking parts." 


C. W. Bunn, General Sales Manager of Electrical 
Research Products, has announced the appointment of 
H. W. Dodge to head the organization's new Mer- 
chandise Sales Department. This